About 6 weeks ago I bought a 5 yr old 90gal with 20 gal sump with water. Good water. About 2 weeks ago I started getting copper colored algae on the sand. It has now left the sand and moved to the walls. It grows back daily, and is getting harder to remove. All water chemistry checks ok. I did put in red slime remover (which I did'nt think was the problem) and it did not help. I did put in some Fiji Gold calcium about 3 weeks ago. I would be thankful for Any help.