alkalinity change

[aeroworm]

I am new to this message thing so I hope that I am doing it correctly. I have recently started up a reef tank after a 20 year lapse. My 90 gallon tank has been set up for about 10 weeks now and has 2 fish, some mushrooms, a "colt" coral, some star polyps, a couple of yellow polyps and a brittlestar. I have Caulerpa racemosa growing rampant and so many protozoa, small crustaceans, and worms growing in there that I rarely feed the fish--they are always fat and healthy looking. The corals are doing well and one of the mushrooms recently budded off. I have been monitoring the alkalinity and pH every day or so to get a feel for what is happening. I noticed that the alkalinity would decrease over a week from 8 to 6 and the pH would rise from 8.2 to 8.4. I figured that this was due to the Caulerpa running out of CO2 and using bicarbonate. I started adding about 8tsp of baking soda to my makeup water and over a week's time that would keep the alkalinity pretty steady. I noticed though, that the Caulerpa was getting pale and stringy and was not growing as well so I did a water change (about 18 gal). The next morning my alkalinity was up to 11 and my pH was 8.2. The Caulerpa turned bright green over the next week and grew like crazy. Over the last 3 weeks the alkalinity has decreased to 7 with no bicarbonate added, and I am trying to use the 2 part additives now but am not very confident in my ability to figure out how much to put in. Right now I am just putting in the minimum. All of the animals continue to look ok.
I would like to know what the water change did to cause this drastic shift. Any Ideas?
Thanks

[Randy Holmes-Farley]

Welcome to the forum and RC in general as I see this is your first post!

I assume that the units of alkalinity that you are using are dKH? If so, the value of 6 is too low (that's 2.1 meq/L). Most people maintain lalkalinity between 2.5 meq/L and 3.5 meq/L (about 7-10 dKH).

A few other comments:

1. The response of the caulerpa to the water change may not have been alkalinity. More likely it liked something that was added (maybe iron) or didn't like something that was reduced in the change (like maybe copper).

2. The caulerpa won't be using up much alkalinity, if any at all. Whether it uses CO2 or bicarbonate as a carbon source, it won't have anywhere to store the alkalinity from the bicarbonate, and will have to release it (perhaps as OH-) if it uses bicarbonate to make organics.

3. Other things in your tank (like coralline algae on the rock, assuming that you have rock) will actively use up alkalinity as they precipitate CaCO3.

4. I'd measure the calcium and see where it is, and then use the two part additives to maintain calcium around 400 ppm and alkalinity in the range of 2.5 to 3.5 meq/L.

[aeroworm]

Dr. Holmes-Farley

Thanks for the reply and Happy New Year.
Yes my units are dKH and I have upped my dosage of B-Ionic to try to correct the low alkalinity. A friend of mine said that I should be adding another buffer also but I thought that part 1 was the buffer? Should I be adding bicarbonate too? The bottom is 4 inches of aragonite sand over a 1 inch plenum. and I don't have much right now that is depositing calcium--the coraline algae is just a few spots here and there, I have no clams or hard corals yet. Just a few small snails and some Spirorbids. Am I going to get too much calcium as I increase the dosage to buffer the system? I was using 20mls daily but I have increased it to 30. Of course I don't want to change things too quickly and it just seems that there should be plenty of buffer in the system. Where is it going?
The reason why I think the Caulerpa is using the bicarbonate is because of the pH increase that I am seeing. I grew diatoms on labeled bicarbonate once and the pH increased steadily until it got to 10 (at that point I harvested it because it would soon crash). Just as you said, the plant using bicarbonate would release OH- . As I understand it, the metabolic processes of the animals and bacteria would tend to lower the pH.
I still wish the big alkalinity increase that I had after the water change made sense. I will feel better about manipulating the chemistry when I understand more what is going on in my system.
Thanks for your input.

[MickAv8r]

The alk increase from the water change would be expected IMO. While you only changed 20% if it was chronically low adding fresh saltwater that has a presumed stable and proper alk level "should" raise it.

I'm wondering if you may be overdosing the 2 Part causing the alk to be driven down.

Randy I have had a hypothesis for awhile now in regards to these 2 Part Solutions. The recommended starting dosage is usually 1 ml per 4 gallons per day. Thats always been the kicker. If this is being added to a new aquarium there is simply no way that much calcium is needed because it isn't being consumed. Now I don't have the formula handy hear at home, however I do know that it can be shown that overdosing CaOH can cause calcium to precipitate out. I have seen NUMEROUS tank water chemistries that come into my store because we do free testing, and a very common one is the aquarist with chronically low calcium and alk dosing massive ammounts of two parts and nothing ever happening OR the calcium and/or alk dropping. In this situation I reccomend the aquarist STOP, do a few water changes and then continue use of the 2 parts but not at the 1/4/day dossage but on an 1/4/AS NEEDED dosage. I've never seen an average reef aquarium i.e. couple SPS, LPS and sofites (mix of eveything) that has ever needed more than some 2 Part added once or twice a week at best. My hypothesis is that overdosing the two parts can lead to preciptation of buffer and calcium as well, through what chemical process I don't know.

[Randy Holmes-Farley]

aero:

<< I grew diatoms on labeled bicarbonate once and the pH increased steadily until it got to 10 (at that point I harvested it because it would soon crash). >>

I'm not sure that I understand what you are saying here, but I'll take one stab at it. If you put sodium bicarbonate in water, and then let it sit in the air, the pH will rise. The reason is that some of the bicarbonate (HCO3-) breaks apart into H+ and CO3--. The H+ then recombines with another HCO3- to make H2CO3. This looses a water, becomes CO2, and goes off into the air. What remains is the carbonate, which results in a higher pH:

HCO3- <----> H+ + CO3--

H+ + HCO3- <---> H2CO3 <---> H2O + CO2


< A friend of mine said that I should be adding another buffer also but I thought that part 1 was the buffer?>

It is. Don't add anything besides the B-ionic unless the calcium is too high and the alkalinity is too low. Maybe I missed it, but did you measure calcium? I think before you conclude that B-ionic alone is inadequate, you need to measure calcium.

<< The reason why I think the Caulerpa is using the bicarbonate is because of the pH increase that I am seeing. I grew diatoms on labeled bicarbonate once and the pH increased steadily until it got to 10 (at that point I harvested it because it would soon crash). Just as you said, the plant using bicarbonate would release OH- . As I understand it, the metabolic processes of the animals and bacteria would tend to lower the pH. >>

Yes and no. If the caulerpa were using bicarbonate, the pH would rise due to the OH- being produced (since caulerpa has no way to accumulate alkalinity). The reason that metabolic processes tend to lower the pH is a consequence of the initial parts of the nitrogen cycle. The conversion of organic nitrogen compounds to ammonia then nitrite then nitrate produces acid which lowers the alkalinity and the pH. If you have a lot of this happening, it can be a factor in a reef tank.

[Randy Holmes-Farley]

Tom:

<< My hypothesis is that overdosing the two parts can lead to preciptation of buffer and calcium as well, through what chemical process I don't know.>>

I agree, though I would extend it to any method of calcium and alkalinity supplementation. The water can only hold so much, and if you dose more than the tank is consuming and more than the water can hold, you will get precipitation of CaCO3.

The question is whether you can actually get values of calcium and alk below natural levels by overdosing something.

Limewater can do this because if you add it too fast, the pH rise converts much of the bicarbonate to carbonate, making it much more likely to precipitate calcium carbonate. Once a significant precipitation event starts, it can continue to cause precipitation to below NSW levels, until the water is just saturated with calcium and carbonate (which is way below normal reef tank levels).

The two part solutions can also do this if added too fast, but are somewhat less likely too since they don't raise the pH as much.

A calcium reactor is much less likely to have this problem because you can't easily add it too fast, and the pH is typically lower.

In most cases. if the person does not see a CaCO3 snowstorm in the tank, I don't think it too likely that such excessive additions will keep calcium and alkalinity at low levels. The slow ongoing precipitation of CaCO3 that takes place in nearly every tank (on heaters, pumps, etc.) will just accelerate if more calcium and alk are added, but the levels still typically remain high. I think this is why dosing does not need to EXACTLY match tank need: a little overdosing just leads to some extra CaCO3 precipitation. Otherwise, how could hobbyists attain perfect balance over the long run between input and output? It's not by careful measurement, IMO.

I do agree that dosing recommendations are almost useless for calcium and alkalinity. The range of need in similarly sized tanks has got to be more than a factor of 10 even considering fairly well-stocked tanks.

[aeroworm]

Thanks again for the input and sorry that it has taken so long for me to get back to this. I wanted to get a calcium reading but have not been able to get to the place that has the test kits for sale. In the meantime, I have found that the pH kit that I have been using is not very good. I found 2 others that had more discernable indicator colors and they are reading 8.3-8.4. The pH kit I was using had very similar colors for 8.4 and 8.8.
Increasing the b-ionic dosage to 30mls per day did absolutely, nothing for the alkalinity--it remained at 6 dKH, however my seasquirt died abruptly(don't know if that had anything to do with it--the other animals are fine). It was time to try something different, so I discontinued using b-ionic for 3 days (dKH stayed the same) and then added 3 Tsp of sodium bicarbonate. The next day the alkalinity was 8. About a half tsp per day maintains this alkalinity. There has been no indication of mass calcium precipitation (no "snowstorms" or sand clumping) but something was preventing the increase in alkalinity that should have occured while I was using the 2-part supplement. And when I stopped adding calcium, my alkalinity increased--so that points to the calcium additive being involved in some type of precipitation, I would think.
I am not really happy about the alkalinity fluctuations that have occured but the critters have toughed it out so far and I am determined to do better for them. I return to my original concern that if I continue to add bicarbonate, then do a moderate water change, what is the chance that I will get a large increase in alkalinity again and what can I do to prevent that?
Thanks Again

[Randy Holmes-Farley]

Aero:

<< There has been no indication of mass calcium precipitation (no "snowstorms" or sand clumping) but something was preventing the increase in alkalinity that should have occured while I was using the 2-part supplement. And when I stopped adding calcium, my alkalinity increased--so that points to the calcium additive being involved in some type of precipitation, I would think. >>

That is a reasonable hypothesis.

<< return to my original concern that if I continue to add bicarbonate, then do a moderate water change, what is the chance that I will get a large increase in alkalinity again and what can I do to prevent that? >>

Once you get the calcium and alkalinity where they should be, and assuming that the salt mix is OK, you should not have these problems using a two part additive. You are much more likely to see big swings using seperate calcium and alkalinity additives, where you are trying to balance things yourself.

Let's see what the calcium readings come out at.

[aeroworm]

Hi I'm back finally.

I was able to get a Kent Calcium Test Kit (I know that there is a better one but could not get to the store that carries it).
My aquarium is 90gal with a deep sand plenum and a protein skimmer.
Calcium is 300ppm
dKH stays at 8 as long as I keep adding 1-2 tsp of baking soda every day.
SP is 1.025
pH is 8.3
Temp is 79F
Ammonia and Nitrate are 0
I have new lights 4x110 VHOs--right now I have 2 40watts and 2 110 watts installed.
The coraline algae is faltering--turning pale and coming off at one spot.
The caulerpa is also turning pale.
I changed 15gals of water last weekend. No alkalinity change.
My colt coral is retracted but everyone else seems to be ok.
What should be my strategy for bringing up the calcium? There shouldnt be that much in there that is using it should there?
Also, do you know if there is any settling of Instant Ocean Salts in the bag? Should the salts be mixed before using part of a bag?

Thanks again

[LoneRegister]

Just a thought.

but you may be adding too much of one, and not enough of the other.

And - as I understand it (and I am not sure I do) you can add calcium to the system up until a certain point - then the calcium comes out, and pulls out lots of extra with it. So, if your systems precipitation level is 400, and you put in 410, it may precipitate out down to 320 or something. Perhaps even more.

However, Alk is critical to bringing up the saturation point for calc. Kinda like the Dew point and water vapor. (Guys - that is an excellent analogy isn't it?)

Perhaps - what you are doing is OVERDOSING the system. I would go with 1ml per 10 gallons on each and see where that takes you. Perhaps it's not that your system doesn't need it. Perhaps it's that you are giving it WAY too much and it's just flying the wrong way.

Perhaps try 1ml per 20 gals and see if you see any changes in the right direction.

Any - just some thoughts based on my readings. Please correct me if I am way off track.

[Randy Holmes-Farley]

Aero:

<< Calcium is 300ppm dKH stays at 8 as long as I keep adding 1-2 tsp of baking soda every day. >>

That rate of baking soda seems adequate for now, but you need calcium too. There are many ways. Calcium chloride (Turbo calcium and other brands) is a fine way for you to start. Once you get it up to 400 ppm, I'd go back to the B-ionic.

[aeroworm]

Sounds like a plan. Thanks everyone for the feedback.