green on gravel and rocks

[fishguy007]

i have had my tank set up now for about 4 months. noticing that my gravel )crushed coral) and the rocks are turning green and red. is this normal and what is causing it.

The protein skimmer is also sucking out alot.

I was told it should slow down AFTER A few months? could i have a problem

i attached a picture if anyone can view it and see what may be happening.