Randy, what's your opinion on Calcium Reactors?

[Oceansize]

I think I already know the answer because I seem to remember finding one of your posts or articles on the subject and my recollection is you are not a fan.

Could you elaborate just a little on the pros & cons of Ca reactors? I'm at a point where I need to either get one of those or set up a dosing system. I've been dosing manually so far and I'm ready to graduate to the next level.

I know you're partial to the 2- or 3-part dosing system, I'd just like to know more about the rationale behind this vs. a Ca reactor. Thanks in advance!

-Barry

 

[Randy Holmes-Farley Verified Community Expert]

I think they are a fine way to go for high demand systems.

This is my blurb on them and other methods:

https://www.reef2reef.com/blog/the-many-methods-for-supplementing-calcium-and-alkalinity/

from it:

Calcium Carbonate/Carbon Dioxide Reactors

Calcium carbonate/carbon dioxide reactors work by removing water from the tank, adding carbon dioxide to reduce the pH to about pH 6.5, and then allowing the more acidic water to dissolve solid calcium carbonate media that is present in a mixing chamber. The water is then returned to the tank with its extra calcium and alkalinity (bicarbonate):

CaCO3 + H+ → Ca2+ + HCO3-

Reef tanks employing such reactors typically run at a pH below that of natural seawater, with typical tank pH values of 7.7 to 8.1. The reason for the low pH is the constant delivery of low pH solution to the tank, adding both excess CO2 and bicarbonate. There is no way around this completely, but some reactors incorporate a second chamber, allowing the liquid to pass over additional calcium carbonate media, making better use of the carbon dioxide that is actually added. Aquaria then blow off this extra CO2 and the pH rises, but the effect is typically not complete, and the pH often stays below what would be the case if the same tank water were fully aerated (that is, equilibrated) with normal air.

The media used is important in these systems, with the aragonite form of calcium carbonate being more readily dissolved than the calcite form (although both work). Also, the nature of the impurities can be very important, as nearly all of the impurities will be dissolved and delivered to the tank. Some of these impurities may be desired by the aquarist (such as magnesium and strontium) and some may not be (such as phosphate or copper). Phosphate in reactor media has sometimes become a point of competition between commercial suppliers of media for such reactors, but I would advise aquarists to be skeptical of some of these claims.

One big advantage of these reactors is that they can be scaled to deliver any amount of calcium and alkalinity needed by any tank. For this reason, they are greatly favored by those who have tanks with a high demand for calcium and alkalinity. Because of the low pH that often results, many of these aquarists choose to dose limewater in conjunction with the reactor, not because the reactor cannot supply enough calcium and alkalinity, but purely to raise the pH in the tank itself. The synergy between limewater and CaCO3/CO2 reactors involves more than just pH. Limewater uses up CO2 and CaCO3/CO2 reactors deliver it to the tank. Together, they combine to keep CO2(and consequently, pH) more in line with natural seawater.

Calcium carbonate/carbon dioxide reactors take up a substantial amount of space, since one needs a carbon dioxide cylinder, a reaction chamber, and a pump. Typically, these systems are used close to a tank, but they could be remote if appropriate water flows to and from the tank could be worked out. Once an aquarist has properly adjusted the reactor system, it requires minimal monitoring for a substantial period. Tank salinity will not increase over time using calcium carbonate/carbon dioxide reactors.

The likelihood of problems from overdosing using such a reactor is minimal. Since the pH is typically low, even substantially elevated calcium and alkalinity values may not cause a dramatic calcium carbonate precipitation event. More likely is just slow precipitation onto heaters and pump impellers. Accidental delivery of large amounts of CO2 to the tank is a concern, but that is a rare accident.

The initial costs of such reactor systems can be considerable, typically about $300-600 for the reactor itself, plus additional costs for the CO2 apparatus. Media costs vary, but a bit over $2 per pounds is typical. That puts the media cost at about $0.30 per thousand meq of alkalinity. DIY ground limestone can be used as media for a tiny fraction of this cost, if you can find it locally. The carbon dioxide cost also needs to be figured in, so that might push the total to about $0.40 per thousand meq of alkalinity.

The primary safety concern for these systems involves the carbon dioxide gas cylinder. Any high-pressure gas cylinder can be very dangerous if the cylinder head should become damaged. So be careful to not drop such cylinders least they become rockets.

 

[Oceansize]

Thanks Randy. I believe your previous comments that stuck in my head were not from a discussion about calcium reactors, they were from a discussion about sulphur denitrators such as the Korallin S-1502 that include some aragonite in the chamber in addition to the sulphur to help offset the effects of the more acidic water that the denitrator produces. In essence, the denitrator is sort of a half-calcium reactor anyway because the purpose of the aragonite in the denitrator is to offset acidification by buffering kH and Ca.

This article you've attached helps explain why I have been having a hard time getting my pH back to 8.3. Since my denitrator is sort of a calcium reactor anyway, I'm experiencing that issue already.

I am using the denitrator with outstanding success, except that it does not appear to be keeping up with my kH and Ca demand even with the aragonite in the chamber, therefore I've been supplementally manually dosing to keep up and hence why I'm looking at Calcium reactors. Yes, I am ready and willing to have both a sulphur denitrator and calcium reactor running side by side. If I do, I will probably take the aragonite out of the denitrator and replace it with more sulphur, as I should be getting adequate Ca and kH from the calcium reactor itself.

So as I understand it, the denitrator lowers pH as a side-effect because it eats up all the oxygen before eating up all the nitrates, and that makes the water more acidic. It is, therefore, a by-product of the denitrifaction, and aragonite is added to offset that side-effect. Whereas a Ca reactor lowers pH on purpose through the use of a CO2 canister in order to create the necessary acidity around that aragonite. So the water in a calcium reactor gets more acidic due to an abundance of CO2, whereas the water in a sulphur denitrator gets more acidic due to an absence of oxygen? Do I have that correct? Does that mean the denitrator is producing CO2 naturally? I know the bacteria in a sulphur denitrator eat up oxygen before eating up nitrates, should I assume that bacteria is producing CO2 as it consumes Oxygen? I've been under the impression that the gas that a denitrator produces is nitrogen, not CO2, but I guess it could produce both? Yes I was awake during high school chemistry so I know most respiration involves turning oxygen into CO2 and vice-versa, I guess I just didn't know if that applied to everything in nature, and assumed that the bacteria in a denitrator is only producing nitrogen as it consumes oxygen, not CO2. Now that I think about it, I probably already answered my own question: as the anaerobic bacteria eats oxygen, it produces CO2, and once that is complete it eats nitrates, producing Nitrogen. If I'm incorrect, please let me know.

I believe your hesitance about using sulphur denitrators with aragonite in the chamber (the ones where no vodka feeding is required) was due to the fact that calcium and alkalinity would not be raised in the correct ratios or something to that effect? For example, if the aragonite in the denitrator were adequately providing enough calcium to the tank, then the alkalinity would be raised too much? Or vice-versa or something? I apologize for my poor recollection. Heck maybe it was a different Randy, lol.

 

[Oceansize]

Reading your article also leaves me with the conclusion that, if I go this route, I will perpetually have slightly low pH. I'm going to assume, based on your comment that calcium reactors are fine for high demand systems, that a tank with pH _consistently_ around 7.7 to 8.1 should not be detrimental over the long term to a reef tank?

 

[Randy Holmes-Farley Verified Community Expert]

FWIW, I don't think that a sulfur denitrator plus aragonite will actually deliver alkalinity. The dissolving aragonite just helps offset the depletion in alk that the sulfur denitrator naturally does, but not more than offset the loss. In fact, probably less.

A CaCO3/CO2 reactor does drive pH down, but folks have great reef tanks in that range. even if it is not optimal for rapid growth..

 

[Oceansize]

FWIW, I don't think that a sulfur denitrator plus aragonite will actually deliver alkalinity. The dissolving aragonite just helps offset the depletion in alk that the sulfur denitrator naturally does, but not more than offset the loss. In fact, probably less.

Yes, that is exactly my experience. The marketing on the Korallin S-1502 implies that the aragonite is not there to raise alkalinity in general, it is there simply to offset the alk-lowering effects of the denitrifaction. But, my testing has proved it is not adequate to keep up with the general alk demand of my tank.

I sort of accidentally tested this effect this weekend: I increased the drip rate on the denitrator to see if I could squeeze some more nitrate-reducing efficiency out of it, and within 24 hours had white cloudiness in the tank. I've determined from prior instances that this happens when the flow rate on the denitrator becomes TOO high. When the flow rate is too high, not all of the oxygen is depleted in the reaction chamber and thus the nitrates are not removed as efficiently. Sure enough, when I tested the effluent and tank for nitrates, the nitrates coming out of the denitrator were higher than the nitrates in the tank, confirming that I increased the drip rate too far. I also tested the tank water for kH during this cloudiness episode and found that my alk dropped MUCH faster than it normally does.

My logical guess is that if the water is moving too fast through the reaction chamber of the denitrator and not as many nitrates are being removed, then this would also result in less acidity than normal in the reaction chamber (not as much oxygen being converted to CO2), and thus less aragonite being dissolved, and thus less Alk buffering.

So yeah, I think I'm going with a Ca reactor. More upfront cost than a dosing system, but less maintenance, supplies, and cost down the line, hopefully.