You are most likely experiencing calcium precipitation. This is when calcium and alkalinity and magnesium are out of balance and the calcium molecules cannot remain soluble. Low
Magnesium levels will cause this or too high of calcium levels will also cause this. It is harmless to your fish but will have an impact if you ever try to grow corals. Coralline algae and other organisms in your tank will impact your water parameters by using up cal, alk
, and mag. These three parameters need to remain in balance.
Do you test your parameters? If you want a clear tank, you will need to monitor Alkalinity, Magnesium, and Calcium.