DSB Heresy

[ldrhawke]

I am posting this in several forums of RC and it follows discussions in other threads.

This is different filtration approach that is sure to cause controversy and sound like heresy to the DSB believers.

What my approach is not: It is Not Jauberet Plenum System and it is Not a conventional DSB. Although it uses somewhat similar process components, it is not the mentioned systems because , for better words, they are stagnant systems. They are dependent upon some sort of natural flux to move waste through there process. It doesn't work.

For now, let us just call my approach, CPW (Controlled Plenum Wasting).

I know the DSB followers will say come back in 5 years when you have proven it works. My response is it does not take years to prove positive results and the system can at any time be made into a Jauberet of DSB by simply not using it, so there is no risk in using it. I also believe for newly established systems, that are set up with CPW, reef keepers will have a much greater chance of long term success.

CPW is based on and assumes the DSB and the Jauberet systems do not work well as biological filters. That is not to say oxic and anoxic biological filtration is not taking place in them, but that it is just terribly inefficient and uncontrolled biological filtration. It assumes at best you can walk a tight rope using them, and make them appear to be functioning, only to have a disaster a few months or years into their operation. If these systems are kept biologically very lightly loaded they may appear to be functioning, when they in fact may be doing more harm than good by slowly or abruptly allowing uncontrolled anoxic septic fluid to flow back into the system or deal with a potential death bomb if you stir up the bed.

If the above is true, why should I not simply use a BB (bare bottom)? The more biological useable and functioning biological surface area you have in a tank the better. It helps to keep the tank stable from the increased biological loading when sudden death or overfeeding occur. It is the same reason the use of live rock has been so successful in making reef tanks possible.

CPW (Controlled Plenum Wasting)

1. It assumes the fluids in the bottom of a DSB are anoxic and are not fully stabilized.

2. It assumes anoxic waste can buildup at a faster rate than the available bed active biological surface can fully stabilize it.

3. It is designed to remove unprocessed or reconstituted nitrates, nitrites, ammonia, phospahtes and other organic waste that accumulates in the bottom of the bed.

4.It assumes DSB and Jauberet designs are not 100% effective in biological stabilization, and infact do cause a major build up of anoxic Hydrogen Sulfide in the bed that does and can leak back into the tank.

5. It is simply a method to compensate for this inefficiency.

6. It improves the DSB biological efficiency by moving fresh food into the zones.

First I will address a major DSB and Jauberet process fallacy often stated.

1.) Anaerobic processing is completely stopped if anoxic fluid( partially oxygenated) moves into a DSB zone and it takes weeks to recover. All of the waste I remove does not show that to be factual.

You do not need or want large low or no flux dead zones in a DSB. You want a positive low transport rate of fresh septic material into and out of these zones. Depending completely on critters in a bed to do this is foolish. Most critters do not like to go into the large anoxic sulfide laden zones that quickly build up.

What is CPW (Controlled Plenum Wasting)? I will given a concise description of how I built my system and how it works. It is not very complex or should it be highly controversial, except for the fact that it may be viewed a heresy by advocates of DSB's. It is really based on common sense. It simply keeps a more positive flow into the bed and not back out into the tank water column.

In my system I have installed a plenum piping system, at the bottom of the bed, with relatively low very small number of orifices. I do use a coarse uniform agronite crushed coral as a DSB media (Carib Sea Special Grade Sand). This is all to assure of a more even flow distribution across the bed. A conventional commercial bottom filter, with is large open area, can and will rapidly short circuit the flow.

On a daily basis I drain the plenum of a couple of pints of anoxic waste that accumulated.

That is all there is to the system.........

I have the drain valve controlled with an X10 switch and my computer. It drains out a small amount every 8 hours.

Set up- Reef Tank: 45g half barrel, 30Hx15Dx30W, 5" DSB with a plenum bottom filter from which I drain 1 couple of pints of waste daily, Carib Sea Special Grade Sand 40 lb, 40Lbs Fuji branch LR, 15 G BB Fuge, Kalk Reactor, Skimmer, Ozone feed.

Why do I say this approach works better than other approaches that try to neutralize all the waste within the bed. It is based on very obvious measured results over two months.

1. What is drained out is always anoxic and has a rotten egg smell. Not something you want to remain in the tank. The fluid drained is anoxic, pH of the wasted fluid is always .5 lower than the water column, three to four times high ALK readings in the wasted fluid; all of which are an indication of continuous biological sulfide processing taking place deep in the bed.

2. When I have purposely allowed even a small amount to this anoxic sulfide laden fluid to re-enter the tank, the tank ORP read out drops like a rock and takes nearly a half day to recover. Even with the addition of ozone into the skimmer.

3. I have stopped making weekly 25% water changes.

4. My ORP readings have never been higher, they are approaching 400 mv. . Infact they remain above the ORP 350 mv set point for ozone feed and are continuing to increase. Little to no ozone is now even being added to the skimmer.

5. My water quality continues to improve, and all of the coral are responding positively to the water quality.

Is the above proof positive that this approach has merit? It does for me. Sure I will continue to monitor and tweek the wasting rate to see if I can improve upon the result. I am sure other will improve upon this approach and I will continue to monitor and post the good and bad.

I have experienced no negatives. My tank is very stabile with very low ORP swings and much more rapid recovery. I no longer do weekly water changes, which was a pain in the butt. The total amount of water removed is a small fraction of that need during normal water changes.

Some of the other potential but unproven positives. (see the attached independent list of negatives from anoxic sulfide processing going on in a DSB.) This RC thread is on going and worth reading. http://archive.reefcentral.com/forum...5&pagenumber=1
________________________________________________

http://www.ozestuaries.org/indicato..._reduction.html

Organic matter decomposition can be a consequence of sulfate reduction in the sediments of coastal waterways (and other aquatic systems) [1]. The process is performed by anerobic sulfate-reducing bacteria. The bacteria require: metabolisable organic matter ; an anoxic environment (or microenvironment); and dissolved sulfate. Hydrogen sulfide gas (H 2S) and alkalinity are generated in the process (see simplified reaction 1).

Consequences of Sulfate Reduction

H2S smells like rotten eggs, and can detract from the aesthetic amenity of coastal waterways when it is released to the atmosphere [2,5].

H2S is toxic to a wide range of aquatic organisms [3];

H2S can inhibit nitrification [4]. When nitrification is inhibited, coupled
nitrification-denitrification is also inhibited.

Ammonium (NH 4+) is released from organic matter during degradation by
sulfate reduction (Equation 3) [6]. Ammonium is a bioavailable and is
readily taken up by plants.

(Eq. 3) 106(CH 2O)16(NH 3)(H 3PO 4) + 53SO 42- “106 CO 2+ 16 NH 3+ H 3PO 4+
106 H 2O + 53 S 2- Iron sulfides ( e.g . pyrite), formed during sulfate
reduction, are an active component of acid sulfate soils (***),
and problems with acid production and drainage can arise if the pyrite
is oxidised .

Iron sulfides cannot bind phosphate . Therefore, when iron oxyhydroxides are converted to iron sulfides during sulfate reduction, phosphate can be released to the water column [9].
______________________________________________________________

The above leaves little doubt in my mind as to why a conventional DSB is a crap shoot and a ticking bomb. I will continue to run my experiment with removing this sulfide rich waste soup to see if a DSB can be made to work. Without a method of removing all of this bad soup from the bottom of any DSB I don't believe they can* work. *(can is relative. I mean eventually fail)

I personally believe your odds at the crap table in Vegas are better than you odds of having a reef tank using a DSB more than a few years before it flips or leaks back into the tank killing everything. If you had a strictly SPS tank with few fish you may beable to stretch the tank life out a few more years.

Phosphate non-binding can be a problem with a DSB, but the biggest advantage of a BB, and only using live rock, is that you have very little sulfate reduction zone to cause an upset. The negative is you have greatly reduced biological processing surface.

With a BB don't have a big hot cauldron of anoxic sufide soup that a DSB can produce. It is loaded with ammonia, nitrates, is nitrification inhibiting , toxic H2S laden, and an oxygen depleting soup building up in a DSB waiting to boil over and snuff out life.

[MarkS]

So, the tank is drilled with the valve below the tank?

[ldrhawke]

MarkS
So, the tank is drilled with the valve below the tank?

NO....not holes in the bottom, see my gallery. The bottom plenum is piped to syphon over the top of the tank and down. I purge air out of it using a reverse flow to fill it first. Once it is filled everytime I open the valve under the tank it pulls a syphon and drains the bottom.

[MarkS]

Cool.

I like this. It makes perfect sense and addresses the problems with DSB's.

[Tat2dBrownDude]

makes sense to me

[MarkS]

Do you do this as part of a water change?

[ldrhawke]

It replaced my 25% weekly water changes. It is actually small daily water change. The advantage is it is removing th most concentrated waste at the same time.

I add a few spoons of salt everyday to the sump to make up for salt and trace elements lost and maintain my 1.026 sg.

At this point I no longer see a need for separate water changes. The water quality has never been higher and the tank more stabile.

The small daily change also avoids the possible rapid S.G. and Temperture swings that a 25% water change can causes if the mix is not perfect, even though the swing has a mostly affect. The rapid change that can occur isn't always positive.

[stevemc]

Sounds like the start of something new and wonderfull that works! I have tried deep sand beds and plenums and found they do as you said, work fine until one day you need to tear it down, because it contains bad stuff. I cant control my phosphates in my DSB tank, and am going to tear down. I didnt quite know what to do, except maybe just a thin layer of sand. I have read a few things here in the past, maybe it was your post, and it gave me an idea, like yours. I'm going to do the same. Thanks! Steve.

[MarkS]

I think I'm going to give this a try in my next tank. What material did you use for the plenum? I did not see it in your gallery. Awesone tank, BTW!!!

[Fredfish]

Sounds interesting. To be sure, there are some long term issues with sandbeds.

I am not sure I understand how this gets around long term nutrient loading in a sand bed.

I thought that the nutrient buildup in sandbeds was in the form of organic solids, not just nutrients in the water trapped in the bed. Draining off liquid wouldn't help with this.

Since the exchange of water between the sandbed and the tank is very slow, I also wonder what happens to the hydrogen sulfide?

My water quality continues to improve, and all of the coral are responding positively to the water quality

Can you quantify the continued water quality improvement? Is it just the orp or is there something else you are measuring?

Also, could you describe how your corals are responding?

THe reason I ask these questions is that I am curious to know what changes in your tank have given you to believe that there is an increase in the quality of the water. The longer I keep a reef tank, the less sure I am that I know which changes in my tank are positive and which are not.

For instance, most people take it as a good sign when their tank stops procuding algae, yet, in the wild, without a huge number of herbiverous fish and other creatures, reefs would produce huge amounts of algae. We generally don't stock the same evel of herbivours in out tanks, so we get excess algae. Algae growth is a sign that we do not have enough herbivours in our tanks, not necessarily a sign of poor water quality.

I have been contemplating a similar change/addition to my sandbed only I wanted to continually drain some of the fluid from the bottom of the sandbed and reintroduce it to the system via the skimmer effectively turning the sandbed into a large denitrator. My logic is that this increases the efficeincy of nitrate reduction by pulling a larger volume of the tank water past the reducing bacteria, increasing the processing capacity. It still dosn't deal with the build up of organic detrirus in the bed though.

By the way, did you read the most recent Reef AquariumUSA? There is a really good picture of the "sand bed" located next to most of the barrier reef in Australia. If you look at the vast amount of sand compared to the reef, you begin to realize that we really do put a very heavy load on our sandbeds and it should not be surprising that there is nutrient build up.

Fred.

[ldrhawke]

http://reefcentral.com/gallery/showp...t=1&thecat=500

I used 1/2" pvc pipe. About 30 (1/32") holes are drilled in it and it was covered with 2 layers of drainage cloth to keep the holes from plugging and to assure of a more even fluid flow across the DSB bottom. The coarse crushed coral covered it.

It is piped so that it can be run in reverse to unplug the holes. I have seen no reduction in flow so plugging is not a problem.

[ldrhawke]

I am not sure I understand how this gets around long term nutrient loading in a sand bed.

I thought that the nutrient buildup in sand beds was in the form of organic solids, not just nutrients in the water trapped in the bed. Draining off liquid wouldn't help with this.

The major premise of using any sand bed is to develop adequate bacteria within it to break down the detritus. Both the resultant finer detritus and bacteria become a food for other bacteria deeper in the bed as well as food for the coral. Draining off the bottom removes mainly unprocessed organic wastes that is now in solution or very fine particles.

Do to the lower pH present in areas of the bed, some people also believe that deposited phosphates may go back into or remain in solution deep in the anoxic bed zones. It is possible some phosphate may also be removed, but that is unproven and just theory.

I used to have a number small pockets of fine detritus that collected in still areas and pockets on the top of my bed. For what ever reason, after starting CPW (Controlled Plenum Wasting), I no longer have any pockets of waste on top of the bed. I am not claiming it is because of CPW. I am just stating an observation.

Also, remember I do not believe in using fine sugar sand. I believe it is far to dense and leaves little open area to allow adequate fluid flow. I use a very uniform coarse crushed coral that is designed for exactly what I want. Pore space for fluid movement to reach deep into the bed

Can you quantify the continued water quality improvement? Is it just the orp or is there something else you are measuring?

Also, could you describe how your corals are responding?

Your are right good water quality is a rather nebulous statement. I have reduced algae growth, because of low phosphate and nitrates is one of my criteria. I had a hair algae bloom just before I started CPW because my phosphate and nitrate readings were increasing. It is one of the reason I started looking for other solutions to maintaining lower phosphate and nitrate.

To be fair, I have also reduced my fish feedings and reduced lighting time, so again I am not claiming CPW stopped my algae growth. But, I believe it has helped.

What I have experienced is close to zero nitrate, nitrite, ammonia and phosphate readings in my water column. I believe the high ORP readings and rate of ORP recover response are significant. For the first time my ORP reading has moved above and stays above the 350mv set point for ozone feed. It used to stay right at 350mv and turn the ozone off and on continuously. As Chemical Randy has pointed out to me the meaning of a high ORP and what the readings indicate are very complex. It also will vary from tank to tank because it has so many variables that cause change.

I do think all agree a high ORP reading is better than a low ORP reading. I am getting my highest ORP readings I have had since setting up the system without the aid of ozone. Also I am getting very rapid ORP correction from its drop when I feed. I feel this is a positive sign, which I do feel CPW has contributed to happening.

I have been contemplating a similar change/addition to my sandbed only I wanted to continually drain some of the fluid from the bottom of the sandbed and reintroduce it to the system via the skimmer effectively turning the sandbed into a large denitrator. My logic is that this increases the efficeincy of nitrate reduction by pulling a larger volume of the tank water past the reducing bacteria, increasing the processing capacity. It still dosn't deal with the build up of organic detrirus in the bed though

Continuous low rate drain back into the tank has been tried before with little success. The conventional commercial bottom filter with a bubbler does that.

1. You do not want to put the waste liquor off the bottom back into the tank. I have found it highly polluted still and even small amounts will cause major negative swings in ORP that are slow to recover.

2. I also consider reprocessing or putting the waste liquor from CPW into further processing , like denitrification. After considering it , it just didn't make any sense, even if I could totally reduce all waste to zero. Why do it when you still should make partial water changes to replenish the strontium, molybdenum, etc that comes with a fresh mix and needed my the coral. I believe partial water changes are good and CPW does this automatically when I waste to the drain.

My sump has a float control for replacing the wasted water from CPW wasting with RO/DI carbon filtered water. Now all I do is add a few spoons of fresh salt mix daily to the sump to maintain the S.G. and replenish trace elements. It is a lot easier, cheaper, and more convenient that doing my weekly 25% water changes.

Keep in mind the whole concept of CPW is simple. Remove waste from where it concentrates.

All the measurements I make indicate I am doing that. There may be other long term benefits; i.e, improving the DSB performance as a bio filter, removing phosphate from the bed, etc. That has yet to be proven.

I do know my coral are all in full bloom and appear happier....if coral can be happy...:>)

I do know my ORP read outs are the highest they have ever been and very stable.

I do know that what I am wasting through CPW is not stuff I want to keep in the tank.

I do know that all I need to do is tell the computer to stop opening a valve every 8 hours for 15 seconds and the automatic drainage will stop. I will then be back to where I was before I started CPW.

What is the risk in using CPW? Zero!

What is the potential upside.....


I like those type of odds....

[Putawaywet]

Interesting concept and I'm certainly looking forward to more info on this as months go by.

But I'm curious about your autotmatic drain setup. Am I reading correctly that your computer removes the set amount of water from the plenum on a daily basis? If so, what happens if there is a mechanical failure during the actual drain process? Wouldn't a stuck valve in conjunction with the X10 module allow the tank to completly drain?

Other than that it sounds like you have a variable alternative to DSB's.

Me thinks this is going to make for some intersting and heated discussions with the mainstream folks

Brett

[ldrhawke]

But I'm curious about your autotmatic drain setup. Am I reading correctly that your computer removes the set amount of water from the plenum on a daily basis? If so, what happens if there is a mechanical failure during the actual drain process? Wouldn't a stuck valve in conjunction with the X10 module allow the tank to completly drain?

Excellent point. There are several ways to address that issue.

The easiest being to use two spring loaded normally closed solenoid valves in series and install a small filter screen in front of both. If one of the solenoid valves should hang up with trash on the seat, the second will still close.

As example, an industrial solenoid valve like the ASCO Series 8260 with a plastic body are normally designed for million of cycles. The chance of both valves not functioning is at the same time is extremely low.

You can also design it so the waste discharge goes into a small stand pipe out side the tank that over flows just below the surface of the tank back down into the drain. That way with a valve stuck open, the most water that could be drained is the amount in the tank between the tank water surface and the top of the stand pipe. That could be kept to a couple of inches, so under failure the tank does not drain more than a few inches of water below the normal water height.

I presently use the first method. Although I could go directly to a drain, I presently go to a quart sample bottle so I can test the discharge wasted. My sample bottle sits in a small dish that drains back to the fuge, if for any reason I should forget to empty it.

[Putawaywet]

Ok, got you now. I'm just leary of a computer to an X10 to a mechanical valve. Somewhere, somehow Mr. Murphy will come a calling.

Well, if this is the beginning of a new trend you're going to have to make sure you get your name in there somewhere. What good is a lagacy if it ain't named after you

Best of luck to you.

Brett

[clsund]

Hawke, as others have said, very interesting and compelling thoughts. Do you have a drawing you could post so more of us could try it out?

[H20ENG]

ldrhawke,
This was done in about 97-98 or so by Tom (arrggh forgot his last name!). He used to write for Marine Fish Monthly.
He used drip tubing and fittings and would only drain a little bit once a month vs daily. He noted all the things wrong with DSBs and Plenums back then, and this was his fix for the plenum.
Not to rain on your parade. Please keep up the testing and improvements! I believe it can only help!
Chris

[ldrhawke]

He used drip tubing and fittings and would only drain a little bit once a month vs daily.

This is not even the same concept. Like most all of the past approaches I have read about, the idea was to remove fluid from the substrate at very low rates and very small quantities. The concept was to maintain zero oxygen and the anoxic condition in the bed and not stop denitrifcation.

I do not believe larged quantities of fluid wasting will stop the anoxic process. In fact it possible that stopping the sulfide reduction, will probably accelerate both nitrification and de-nitrification. Hydrogen sulfide stops both nitrification and de-nitirification.

My concept is to remove enough fluid to reduce or eliminate the anoxic sulfide reduction process as well as flush out unstabilized waste building up or remaining.

By reducing the amount of hydrogen sulfide or stopping the reaction, hydrogen sulphide and the other contaminants such as metals dissolved in the rotten egg soup, are less apt to bleed back up into the tank water column.

Also, many of past process that removed small amounts of waste from the substrate simply put the wasted fluid right back into the tank or attempt to reprocess it.

Dripping or removing a little waste once a month or even dripping daily will not have the same end result, not even close.

I love analogies...... the difference in removal quantity. I flush a pint out quickly. it would be like comparing the results when flushing a comode by using a squirt gun with quickly dumping couple of gallons in from the resevoir tank. It has a dramatic effect on the results.

Not to rain on your parade. Please keep up the testing and improvements! I believe it can only help!

Reefers are the most hard headed opinionated group on the WEB. There has been a thunderstorm of reponse since I started discussion the issue You've been nice.

Keeping you up to date. I am wasting nearly a quart a day. I have had a positive response the last few days.....The samples collected no longer have the rotten egg smell that they have had for weeks. This obviously leads me to believe sulfide reduction is slowing down. Hopefully nitrification and de-nitrification will now have more space and food available to increase.

althoght, the importance of efficient biological processing the bed is reduced when using CPW, because the waste is simply dumped in the drain, but a more efficient biological process in the bed wouldn't hurt anything. It would help assure if a rock is picked up or the sand stirred, a major upset is less apt to occur from the release of phosphate and nitrate back into the tank

Wasting a quart a day is only about 1:250 of my tank volume. I will continue to test to find the optimum quantity to flush.

I have stopped my 15% weekly water changes. This was 5 times the amount I am presently using to flush the plenum with.

[ldrhawke]

Hawke, as others have said, very interesting and compelling thoughts. Do you have a drawing you could post so more of us could try it out?

Thanks.....I will work on a drawing for the process component layout and post it in my Gallery and let you know.

[Putawaywet]

Chris,

You're not thinking of Thomas Frakes are you????

Brett

[Fredfish]

OK, so if I understand correctly, since you started this wasting, Your ORP has gone up, nitrates and phosphates have gone down, though this is also due to reduced feedings, algae growth has slowed/reduced.

Did you have any plans to increase your feeding back to previous levels to see what happens to your water parameters?

It is most interesting that the rotten egg smell is gone. I was wondering if you were draining enough liquid from the sand that it would have a permanent effect on the bacterial makup of the bed. It obviously does.

AK! Whenever I get involved with these discussions I end up with more questions than answers. Is there a relationship between nitrogen based reduction and sulfer based reduction? From my reading on coil denitrators, I got the impression there was; that sulfer based reduction started to happen once the nitrates had been completely reduced.

By the way, the link to the OZestuary site is broken. I couldn't find the page you were refering to. Interesting site though.

Continuous low rate drain back into the tank has been tried before with little success. The conventional commercial bottom filter with a bubbler does that.

True, but, in terms of nitrate reduction, the flow rate is critical. A conventional UGF probably has to high a flow rate to make the bed an effective de-nitrator. From what I understand, if the flow through the "denitrator" is to high, nitrogen reduction is incomplete, and you end up going backwards, converting nitrates back to nitrites.

The idea is to get the flow rate through the sandbed to the point where nitrates are completely reduced, but high enough that sulfer based reduction does not happen. That should mitigate ORP issues. It does not address nutrient export the way wasting does, but I plan to use an ATS style filter for nutrient exports.

I must say I find the idea of doing water changes using your system most compelling. Why not do water changes where they will do the most good?

It will be interesting to see how your system progresses over time.

Fred.

P.S. I am still interested in hearing what has changed withyour corals that leads you to conclude that they are more healthy.

[H20ENG]

Brett,
I dont think it was Tom Frakes, not 100% though. I need to dig out those articles.
ldrhawke,
I am curious that now you are not getting any H2S smell, that you may be overoxygenating the bed, thus turning it into a very slow UGF. Obviously you are testing the "liquor" (Oh yeah, I remember my wastewater days ), but how about DO levels?
Just thinking there may be too much of a good thing. At worst, it'll diminish the denitrators in the bed.
Forgive me if you are already on it, just thinking aloud
Chris

[ldrhawke]

Just thinking there may be too much of a good thing. At worst, it'll diminish the denitrators in the bed.
Forgive me if you are already on it, just thinking aloud

Can't have too much of a good thing if I am using the DSB mainly as a sink, and secondarily as a biological filter. I really don't care if denitrators diminish. When people stop trying to figure out how CPW is interfering with possible biological processing in the bed, they will have a better idea of what it is doing.

The concept of CPW is to maintain the aerobic processing in the upper area of the bed and also maintain a positive flow into the bed. I have not been measuring DO. It would be interesting but not a driving number.

The idea is to remove nitrates, phosphates, hydrogen sulfide and other organic waster that collects in the bed and also keep it from being released back into the tank. I am hoping it will improve the nitrification process by feeding it better and give it back the space that sulfate reduction is using up.

Accepting the fact that waste does accumulate in a DSB, it is also important to have adequate flow to remove it and not let sulfate reduction become dominate, which will stop the nitrification and denitrification that may be present. CPW will also help to assure that if the bed is disturbed what is release doesn't reap havoc and sudden death.

The reduction in rotten egg smell from wasting a quart a day is indication to me I am heading in the right direction.

What a lot of people are missing is the important of the physical method to accomplish this. It makes all the difference in the world as to the CPW process working well or not working. If you do not harness the natural behavior of fluids to follow the path of least as they are removed from a DSB, the chances of CPW working are greatly reduce. This is a major key success. I am applying some of the same hydraulic principles I have patented in composting.

Obviously over time and with more people using the concept we can start to narrow the band on the volume of the wasting and frequency. I would not be suprised if the volume of CPW increases, simply to assure of adding back trace elements in fresh salt mix. CPW may not be controlled by the minimim volume required to make a DSB a positive element in a reef tank and not the negative one that many people view it as now because of it's acting as waste collection sink that eventually boils over.

[H20ENG]

What about nitrate accumulation then, if the lower bed begins to lose its reducers? I believe that the "good" denitrification takes place without going as far as producing H2S. I understand your theory, but it seems you can do both- drain off the accumulated waste and do it slowly enough that the DSB can still denitrify.

[Shoestring Reefer]

ldrhawke-
One reefer has been using a DSB with plenum for 9 or 10 years successfully. I believe he is "aged salt". I don't know if he has flow through his plenum or not, but he may be worth talking to.

Also, you state (simplified) that using the plenum/DSB system and removing water from the plenum will help prevent phosphate from being removed; the widely believed problem with DSBs is phosphate buildup, and I have heard little about problems with H2S buildup (not that it doesn't happen, H2S just may be the cause, and reefers care about the phosphate). That's an interesting relationship, it may explain things.