I have a 120 that has been running for almost 2 years. It's a mixed reef with sump and no protein skimmer since it broke a month ago. I use reef crystals salt and have not dosed anything in about 5 months. My calcium is at 500 and has not changed. I test either 2 different Red Sea test. Just wondering how it doesn't go down.
Calcium not changing
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Randy Holmes-Farley
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What creatures are in the tank? Mostly soft corals? They do not use calcium and alkalinity.
Alkalinity will always show depletion and need supplementing before calcium. So if you are not dosing alk, you typically need not dose calcium since they are used together.
Have you measured alkalinity? Maybe it is low and limiting calcification.
Alkalinity will always show depletion and need supplementing before calcium. So if you are not dosing alk, you typically need not dose calcium since they are used together.
Have you measured alkalinity? Maybe it is low and limiting calcification.
Randy Holmes-Farley
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So the water changes (or additions you are making, perhaps without realizing it, in top off water or anything else you add) are able to keep up with the calcium and alkalinity demand. 
If hard corals or coralline algae begin to grow more rapidly, you'll first notice it in a further drop of alkalinity.
If hard corals or coralline algae begin to grow more rapidly, you'll first notice it in a further drop of alkalinity.
Randy Holmes-Farley
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That sounds like a good plan.
