Why is my calcium level rising?

My calcium hardness level seems to be increasing and I am not sure why.

Here are my stats:
FC 20 (Recently SLAMmed)
CC 0
Calcium 425 (was 350 a week ago)
Alkalinity 70
CYA 70
PH 7.5

1) Why is my calcium creeping up?

2) I have read that high calcium is not a problem if you keep your PH down. Could someone explain?


TFP Expert
LifeTime Supporter
Jun 7, 2011
Midland TX
Hi Louis and welcome!

That is too much increase in one week. You have either added a Calcium source such as a Calcium Hypolchlorite Chlorine "shock" or you have some testing/sample variation. Calcium does increase on its own through water evaporating and refill, but that is too much in one week. Minus the Cal-Hypo, I'm going for test variation here. This is presuming you haven't just changed your refill water source, but I do not imagine that's the case at all is it?

Your last statement is mostly true, there is just more to it than that. With your levels, it would pretty much be the case. Keeping the pH correct is the most critical factor dealing with Calcium scaling issues, which I presume you're concerned with. Let's see what we can figure out with the recent change you are seeing first.

PS- Please tell me what test kit you have, and how you arrived at 425.
Jul 20, 2016
Boca Raton, FL
Hi Patrick,

Thanks for your reply and advice!

I have only added chlorine bleach and sulfuric acid in recent weeks - no calcium added, no water added either recently.

I am guessing this is testing variation - perhaps user error.

I am using the TF-100 test kit, which I have been using for about 8 months.

I counted 17 drops of R-0012 today to change the color to blue. In recently weeks it only took 14 drops.