High demand for Alk/Cal?

[SA057]

Randy, I have been using your two part supplements for about a month now and have some questions. For about two weeks I could raise my Alk to about 9dkh and my Cal to 450 but within 24 hrs my Alk could drop to 6 or 7 (Mag stays at 1250)? For the past week I have been checking my Alk/Cal at 8am and 8pm. I have been add what I think are large amounts of both to maintain acceptable levels, 200-300ml per day. My Alk seems to drop in just a few hours. I have been dripping Calk (1tsp/g) for months but went to 2tsp/g about two weeks ago. Your suggested starting doses indicate 1-2ml/g. What causes my high demand? If I have to add 150-200ml of your recipe #2 to my 50-55 gals total water is that high? I also mixed the recipe #1 and used it some (lesser amounts) because my PH stays about 8.1 and I don't want it to go up or down too much.

[Randy Holmes-Farley]

Can you describe what is in the tank in terms of calcifying organisms? (coralline algae, SPS corals, clams, etc)

It is not unusual to have alkalinity drop by 1-3 dKH or more per day. :)

[SA057]

Thanks for the reply, I have mostly small corals, one sps, several pulsing xenia stalks, 2 mushrooms, sun coral pagoda coral and a candy cane coral. I have huge amounts of coralline growing everywhere. No clams several shrimp and crabs etc. I know the coralline takes lots of Cal but I don't understand the rapid drop in Alk? Lastly, I used concrete for my base rock with live rock on top. The tank has been running for about 6-7 mothns with everything growing and thriving. I just can't get this Alk/Cal thing to balance.

[Randy Holmes-Farley]

Coralline and all calcifying organisms use 1 meq/L (2.8 dKH) of alkalinity for each 20 ppm of calcium that they use. It goes into depositing calcium carbonate. The carbonate part takes up the alkalinity.

[SA057]

So my tank can be using 60ppm Cal and 3dhk Alk per day and that is not excessive considering the large amount of coralline growth?

[SA057]

Also if my PH is normally about 8.1 which recipe should I use 1 or 2? Which will have the greater PH impact?

[Randy Holmes-Farley]

60 ppm calcium is excessive. 20 ppm calcium and 3 dKH is not especially unusual. :)

If the pH does not get above 8.1, I'd use recipe 1.