CaOH only system w/ CO2 addition

[thackray]

KALKWASSER ONLY SYSTEM WITH SUPLIMENTAL CO2 ADDITIONS

I am operating a 70 gallon closed system reef tank with a hang-on-the-back refugium. Kalkwasser additions when the lights are off provide the calcium and alkalinity requirements. Since small polyp stony corals are my interest, I anticipate that as the tank matures (it’s just a few months old at this time) my calcium and alkalinity needs will grow. I would like to avoid using two part systems (expensive, salinity increases, additives I don’t need and time consuming) and I can’t easily use a calcium reactor (closed system) and they have their problems also.

By controlling the evaporation rate (controlled fans) I can make “room� for as much kalkwasser as I need from a calcium/alkalinity demand standpoint. However, kalkwasser consumes carbon dioxide from the tank water to complete the conversion of free hydroxide ions to carbonate ions and at some level of kalkwasser additions, the carbon dioxide is depleted. This leaves free hydroxide ions which cause the pH to rise. (pH being a measure of the balance between the hydrogen ions and the hydroxide ions).

The fluctuation of pH due to the interaction of carbon dioxide and hydroxide is seen in the diurnal pH changes normal to our reef tanks. When the lights are on photosynthesis dominates using up carbon dioxide which frees hydroxide ions from the alkalinity complex so the pH rises. With the lights off, respiration dominates producing carbon dioxide so the pH drops.

The presence of a refugium makes a “kalkwasser only� system even more difficult since it is constantly (lights always on) using up carbon dioxide.

The solution would seem to be a small addition of carbon dioxide to the tank water from an external source preferably during the day. An “all kalkwasser� system consisting of a 1) kalkwasser drip, 2) fan controlled evaporation and 3) a means of introducing external carbon dioxide into the tank seems obvious to me but I have never seen anything written about it. Either there is something wrong with this idea or somebody knows something about it since I doubt that I’ve discovered something.

If this system works, what is the best means to introduce the carbon dioxide? It seems to me that an air stone would not work because there is so little carbon dioxide in the atmosphere (0.033%). Could one put a regulator on a carbon dioxide tank and bubble the gas into the tank through something like an air stone? I bought a calcium reactor for a larger sump type system to be set up later. It has a means to introduce carbon dioxide into the reaction chamber. Could that be modified for my closed loop tank?

Frankly, I’d like to operate my (as yet to be set up) larger sump type tank on a “kalkwasser only� system so the limitations and/or set up tips for what I’ve described is of great interest to me.

[Randy Holmes-Farley]

Many folks use limewater (kalkwasser) with aeration as the only source of CO2 (myself included). However, I agree that if you really want to push the limits with limewater, that either tremendous aeration or a CO2 source would be desirable for keeping the pH from getting too high.

I believe that many folks in Europe use such systems, or at least have in the past. I do not know exactly how they introduced the CO2, however.

I would expect that a CaCO3/CO2 reactor without any CaCO3 media would be perfect for adding CO2. It would be better than an airstone with CO2 coming from it, but that would likely work as well.

For that matter, CaCO3/CO2 stystems usually drive the pH too low in aquaria, so if you have one, operating it normally and using a large amount of limewater might end up with a still reasonable pH.

[thackray]

Randy,

Thank you for your response. My long term goal is to automate my system as much as possible.

I bought a calcium reactor for my proposed 150 gallon sump type system hoping to balance its acidic tendencies with kalkwasser additions. Operated by hand with daily adjustments such a system is practical. But I think any algorithm for automatic balancing of calcium, alkalinity and pH with this system would be quite complex requiring computer control. Furthermore, from what I read, the calcium reactor may not act in a consistent manner if it is cycled thereby complicating automatic control.

As you have stated in your articles, kalkwasser can be mixed in large quantities allowing unattended dosing over a week or more. In a typical tank the kalkwasser dosing requirements would not vary significantly over a week or more and as long as the evaporation rate exceeded the kalkwasser dose, this process would be “automated� (an additional automatic RO make up water system would also be necessary since the evaporation rate would need to be slightly larger than the kalk dose rate). Since this process results in an increase in pH it remains to find a process that decreases pH preferably without affecting alkalinity. One process is CO2 addition.

With some form of CO2 injection I could monitor my pH electronically and simply turn on the injector when the pH exceed a certain level. With some hysteresis this controller would turn the injector off after the pH fell a certain amount. If the CO2 injection is slow but adequate, such a system would cycle on and off during the day as needed. The resulting system would be hands-off for at least a week with only a single on-off type controller (other than the RO make up controller which would be on the tank anyway). From the principal of conservation of alkalinity (which I learned from your article), we also know that pH control via CO2 will not affect the total alkalinity.

Colleagues have suggested using vinegar either mixed with the kalkwasser or added directly to the tank. Neither of these approaches facilitates automatic control. Mixing vinegar directly will simply result in different effective pH. No pH control is achieved or possible with out mixing up another batch. Injecting vinegar in response to pH variations seems possible but the control loop would be complicated (perhaps impossible). This is because vinegar acts to reduce excess pH in two ways (as you have stated) 1) it has a proton which combines with the hydroxide ion and I assume this reaction is quite fast and 2) it feeds bacteria that subsequently produce free CO2 molecules and I assume that this process is slow (perhaps days). Since the second process actually contributes more to the pH reduction that the first process we can say that the pH reducing effect of vinegar injection is a slow process. Since the pH is most likely to rise after the tank lights are turned on at say 8:00 AM, in a tank whose pH is being held on the high side, you would probably want to begin controlling pH as early as 12:00 noon. This would not be possible with the vinegar system. Another negative is the vinegar system’s reliance on bacteria (specialized?) and possible by products.

I’m still hoping someone can educate me on the means to directly inject CO2 into my tank.

[Randy Holmes-Farley]

bought a calcium reactor for my proposed 150 gallon sump type system hoping to balance its acidic tendencies with kalkwasser additions. Operated by hand with daily adjustments such a system is practical. But I think any algorithm for automatic balancing of calcium, alkalinity and pH with this system would be quite complex requiring computer control.

I've never used a CaCO3/CO2 reactor, but I haven't been lead to believe that they are all that variable. It would be easy enough to put limewater on a pH controller, and let the CaCO3/CO2 reactor run at a single setting 24/7.

With some form of CO2 injection I could monitor my pH electronically and simply turn on the injector when the pH exceed a certain level.

Yes, that is a fine plan. :)

I agree that using CO2 has advantages over using vinegar.

Here is a site with links to DIY CO2 injector systems:

http://ozreef.org/diy/#CO2_INJECTION

[thackray]

Randy,

The variables “kalkwasser� and “CO2 injection� are orthogonal. That is, kalkwasser adds only calcium and total alkalinity and CO2 injection only reduces the pH with no effect on calcium and total alkalinity. A calcium reactor running continuously adds a fixed amount of calcium and total alkalinity but using kalkwasser to control pH also adds calcium and total alkalinity. Therefore it becomes impossible to accurately control both calcium/total alkalinity and pH.

[Randy Holmes-Farley]

Well, mathematics aside, many folks do just that. I agree that it is not as simple and clear exactly how much of the different things to add, but it still seems to work out OK. The amount of limewater needed to bring the pH up into a desirable range (when using a CaCO3/CO2 reactor) is usually reasonably small, and the CaCO3/CO2 reactor delivers most of the calcium and alkalinitiy in most such cases.

Still, the plan that you have shuold work fine if that is the way that you prefer to go. :)

[thackray]

Randy,

My hope in starting this thread was get your imprimatur on the CO2 injection scheme so that I could show it to my skeptical partner who thinks I’m going to kill everything in the tank with my crazy ideas. We started a reef tank together just a few months ago. She has been reef keeping for years and I just got started this winter. I offered to be the plumber and to try to learn something about water chemistry. The first people I ran across that addressed the science of water was Delbeek and Sprung and Fossa and Nilsen. But it wasn’t until I found your articles on line that it all began to come together for me. Virtually everything I know about water chemistry I learned from you.

I tried to be as detailed as I could in this thread for my own records and for any readers that might find this scheme interesting. For the sake of completeness I wanted to point out the independence with respect to calcium/total alkalinity of the variables “kalkwasser� and “CO2 injection� and to distinguish this in theory from the interrelated variables “calcium reactor� and “kalkwasser�. I only meant to imply that in theory, the calcium reactor 24/7 with kalkwasser additions would be harder to control. As you point out, people are running this system so in practice it is viable.

Our present tank has no possibility of a calcium reactor (closed system and space limitations) so I needed to find a simple pH control mechanism that would work with kalkwasser only. The benefits of high dose kalkwasser additions seem legion with few side effects. The other systems all have caveats.

We will try this system over the next few weeks. I’ll post our progress.

Again thank you for your time and expertise.

[Randy Holmes-Farley]

I certainly don't think it is a crazy idea, and as I mentioned, some folks do use it. As you put it together and begin to use it, let us know how it goes. Perhaps we can help witj an issues that arise, and perhaps we can learn from your experiences. :)

Again thank you

You're welcome. That's what this forum is for. :)