calcium and pH low. please help


New member
My calcium dropped from 440 to 340 over 2 weeks. The pH also dropped very gradually from 8.2 to 7.98-8.01. When I check for phosphate it shows that it is very low. I have two phosphate reactors which work great! Before the reactors the phosphate was at 2. Now it is between 0 - .03.

I did a water change and added some calcium to try and raise the calcium, but it isnt getting any higher. The pH also is not getting any higher, i added buffer and it raised from 7.87 to 7.98. Not sure what to do to get it back to 8.2 gradually so that it doesnt harm my star fish or corals.

I have like 8 hard corals. About 10 soft corals. 3 anemones and about 10 fish. A few shrimp and a few star fish- Just in case you need to know

thnx for your help :)

Randy Holmes-Farley

Reef Chemist
Premium Member
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That's a pretty big calcium drop to be due to consumption. I expect it is mostly measurement error, or due to the water change, or due to excessively high alkalinity. What salt mix did you use for the water change? What salinity?

Stop adding buffers. That is not a good way to control pH, and it may be driving down the calciuum as you push alkalinity too high and cause precipitation of calcium carbonate.

What is the alkalintiy?


New member
the alk is at 3.5. i use red sea salt. and on the salt container it says the salinity is 30.6 ppt for 420 ppm calcium. not sure what that means.
can it be because of iodine. i recently ran out and need to purchase more.
i add magnesium on a regular basis.

about 5 months ago the calcium was at 240! something happened in the family, and now we take care of the tank and had no idea of all this chemical knowledge we needed to know. we added magnesium and the calcium raised automatically. but now i added magnesium and nothing is happening.

the test kits are fine i believe. they have been accurate all along, and we have become very good at knowing how to test everything.