Ca/Alk consumption rates

[Hawkdl2]

Being a bit compulsive, I have been trying to calculate my tank's actual consumption rates for calcium and buffer. I wonder if anyone else has tried to quantify these parameters - recognizing that calcium, if not also alkalinity, changes depend very much on the types and numbers of organisms in the tank.

As a second issue, I'm curious as to the most recent thinking regarding chronic use of CaCl vs. CaOH on the long term health of a reef aquarium.

In order for me to maintain Ca and Alk levels I drip a saturated CaOH (Kalk) at a rate of approximately 0.5gal/day = ~8ppm/day, but also pump CaCl at a constant rate of ~4.7g/day = ~9ppm/day. Buffer (sodium carbonate and bicarbonate) is also pumped at a constant rate of 0.73 meq/day (11.4 g/day). Even at this rate, I recently had a calcium crash and levels plummeted within a week to <320ppm from a norm of 420ppm. I have been supplementing my standard additions with 5g CaCl twice per day (20ppm total/day). Levels are back after a week to ~410. pH remains steady at 8.2+/-0.2 over 12 hours. The tank is 50g medium stocked sps/lps and softies, etc.

Is this regimen sound and how does it compare to other apparent consumption rates. i.e. my tank seems to be consuming ~20ppm/day Ca and 0.75 to 1 meq/day alkalinity.

Does anyone else calculate rates for their tanks?

[Randy Holmes-Farley]

Hawkdl2:

I've not seen anyone calculate calcium or alkalinity consumption rates based on the types of organisms present. I think it depends on too many factors (lighting, temperature, water purity and availability of nutrients, exact size of corals, water flow, etc. etc..

Some people have calculated consumption rates over time based on what they add, and have compared that to values for natural reefs. Craig Bingman discussed this somewhat in one of his articles, and also goes on to answer your second question about what happens with long term use of CaCl2 in such situations. I'm away from my usual setup, but I'll try to provide a link.

Overall, the conclusion is that a small amount of such additions, even chronically, is not problem, especially if you change water at a typical rate. OTOH, heavily calcifying tanks with few water changes quickly get skewed when using only CaCl2.

FWIW, the rates that you have seem consistent with what others with similar tanks report, so it seems reasonable to me. In thye end, those with rapidly calcifying tanks often turn to CaCO3 reactors to keep up.

Personally, my tank does fine without one, and doesn't even need fulls trength limewater, but my tank calcification is in the low to middle range, and my evaporation is high.

Finally, and least importantly, calcium hydroxide is Ca(OH)2. I have no objection to abbreviating it, but some people might get confused by CaOH and think that is the actual chemical. It's important when one is thinking about how much alkalinity and how much calcium comes from limewater.

[Randy Holmes-Farley]

Here are the promised links. They are right on point for your questions:


Calcification Rates in Several Tropical Coral Reef Aquaria

http://www.animalnetwork.com/fish2/aqfm/1998/mar/bio/default.asp

Simulating the Effect of Calcium Chloride and
Sodium Bicarbonate Additions on Reef Systems

http://www.animalnetwork.com/fish2/aqfm/1998/dec/bio/default.asp

Additional Simulations: The Combined Effect Of Calcium Chloride
/Sodium Bicarbonate Additions And Water Exchanges

http://www.animalnetwork.com/fish2/aqfm/1999/feb/bio/default.asp

[Hawkdl2]

Randy,

Thanks very much for the links and sorry for the sloppy chemical formulae. The articles are precisely what I was looking for. I'll try to digest them this weekend. One question, albeit before perusing the articles for the answer, is I don't quite see the logic in Craig's recommended dilutions prior to water replacement. It would seem that while Cl and Na ions are in fact accumulating, that if one assumed top-offs were occurring, a dilution followed by a replacement would result in a long term reduction in other ion concentrations.

Larry

[Randy Holmes-Farley]

Larry:

I think Craig is referring to water changes independent of the calcium chloride and sodium bicarbonate additions. Such as a standard 10 % water change per month, etc.