Coral chip might be the problem. Anyway, I would advise you against using corals chips as buffers in your tank. Cuz after sometime Coral Chip will trap deritus and contribute to your NO3 problems. Also the Calcium from the Corals Chip cannot be adsorb by Corals as such no use.
Once you remove the Corals chips, I believe your Calcium will drop to a manageable level with some partial water change.
Coralines algae will prevent nuisance alage from grow on it. Also, Coralines are generally a good indication of your water parameters.