I'm not understanding my test results...

[vpierce3]

Just saw that you made a testing error. So just take my post above for what it’s worth.

 

[Randy Holmes-Farley]

Really... I would think you would begin getting precipitation at those levels...

Well, the chemistry is fairly simple, and calcium is not a big driver of precipitation within the ranges we normally see.

All of these have identical propensity for precipitation of calcium carbonate:

1. pH 8.1 alkalinity 7 dKh, calcium 500 ppm
2. pH 8.1, alkalinity 8.3 dKH, calcium 420 ppm
3. pH 8.18, alkalinity 7 dKH, calcium 420 ppm

while to get a much bigger propensity, these three are also identical:

A. pH 8.1, alk 7 dKH, calcium 840 ppm
B. pH 8.4, alk 7 dKH, calcium 420 ppm
C. pH 8.1, alk 14 dKH, calcium 420 ppm

Thus, you can see that within the range of levels attained by reefers, folks are far more likely to have pH and alk be big drivers of precipitation, than calcium.

I show how these sorts of things are calculated here:

What is that Precipitate in My Reef Aquarium? by Randy Holmes-Farley - Reefkeeping.com

 

[Randy Holmes-Farley]

8.0-8.1 pH is low? Okay... what do you suggest as a target range?

pH 8.0 to 8.1 is fine for a reef tank, but it is below ocean averages, and most notably and why I mentioned it, that pH range is far, far less likely to result in precipitation of calcium carbonate than are higher pH values ( pH 8.3+), for the sorts of reasons discussed in my post right above this one.

 

[Randy Holmes-Farley]

Okay, 500 ppm on Calcium is a testing error. And I'm guessing that the relationship of calcium to the other numbers in the chart make a calcium of 500 impossible?

Yes. It cannot jump up and down on its own without a big change in salinity.

Also, by dosing kalkwasser, each 20 ppm rise in calcium is accompanied by a 2.8 dKH rise in alkalinity (at least in the short term of a few days). If the alk rise is missing, the calcium rise is likely an error.

 

[Dom]

When you said hyper-filtration, that makes me wonder what your no3 and po4 are at….especially po4. Without enough nutrients, the corals and other stuff won’t be able to metabolize the calcium in the water. This can cause the Ca to shoot up and dkH to drop.
This is what happened in my tank.
My po4 was at zero so I started dosing trisodium phosphates. Then I saw an explosion in coral growth. I brought my dkH up (which raised my pH) and the Ca came down on its own. Now my tank is stable.
Everything needs to be balanced…..including nutrients.

While I can't provide actual numbers, tank appearance indicates the presence of nutrients.