I'm having Calcium Lvl problems

[wwfstyle]

Last week my Cal lvl was almost 500. With out doing water change or additives it has dropped down under 200! I'm confused on why it dropped that fast. About 2 to 3 weeks ago I bought a Tiger Deresea Clam and it looked nice but now not so great. Could this be the problem my clam absorbing the calcium faster then I test? Need to start a Kalk drip system?

 

[promisetbg]

The tank inhabitants are using the calcium. That is why it has to be replaced and maintained at a constant level. I keep mine at 450, with DKH at 11.2.

 

[reefnut]

What is your alkalinity level?? Are you adding a buffer??