If our Salt Water Reef aquarium calcium levels test at 500 mg/l, is that too high, and what do we do if it is?
A calcium level of 500 mg/l is higher than most people run their tanks at but as long as your alkalinity level is also running high it may not be an issue. When high levels (or low levels) of calcium occur in the tank and are out of balance with the alkalinity within the tank, that is normally where this becomes an issue.
Have a look at this article about Calcium and Alkalinity for more explanation. Below are a paragraph from the article that is very helpful:
At the same time that calcium is measured, alkalinity levels should be measured as well. There is a strong relationship between calcium levels and alkalinity that should not be neglected. If the calcium levels get high (over 500) there is a tendency for alkalinity to drop. Conversely, if alkalinity levels get too high, calcium levels will tend to fall as calcium precipitates out. Therefore, check for a desired calcium level between 400 and 450 ppm, and alkalinity levels between 2.5-3.5 meq/L (7-10 dKH).
If you are using a calcium reactor, dosing kalkwasser or using some other type of calcium supplement I would suggest dialing them back. See where you alkalinity levels are at as well, hopefully they are on the higher side as well (to be in balance with the calcium levels).
My best solution would be to do some weekly water changes of between 30-40%. Most salt mixes should mix at a calcium level between 360-420. Doing the water changes should help to bring the calcium levels down and hopefully also bring the calcium and alkalinity levels into balance if they aren't already.