Why does my fish tank rocks and glass keep turning green?!?

I have a 55 gallon fish tank with 3 silver dollars, a african knifefish, an angelfish, and 2 alge eaters. My tank for sometime was fine didn’t change color. Then after awhile the rocks started turning green along with the glass. I thought it was just from like not having a good cleaning. (i mean i was suckin the poop and rocks every 2 weeks. I asked the pet store they said it might be because of the sun coming thru the window causing the problem. I moved the tank downstairs and within 2 weeks the same problem. Its hard work to empty the tank to clean it so i don’t want to do this all over again for the same results…..ANNYYY help anyone?!