Do calcium and phosphates correlate in any way?

[Reefkeepers Archive]

Question for @Randy Holmes-Farley, a few weeks ago my calcium was at 500, a bit high for what I desire so i turned down dosing. I noticed my po4 at that time always tested 0.03 when before the elevated levels it was 0.06, I had not changed my feeding schedule whatsoever. I would ignore this if it wasn't for the fact that now my calcium is back down to 430 and my po4 is 0.06 again... I have not changed feeding whatsoever, if anything im feeding less, same maintenance routine and no water change system as usual. Do po4 and calcium correlate in any way @Randy Holmes-Farley?

 

[Randy Holmes-Farley Verified Community Expert]

My expectation is that the phosphate changes are unrelated to the calcium changes, but it is not impossible for there to be some precipitation of calcium phosphate, or phosphate on calcium carbonate, that forms locally where the calcium concentrate hits the tank water.

That precipitation effect is believed by some to be significant when dosing kalkwasser, since all of calcium, alk and pH are locally high in that scenario.