Black Algea? Help

I have taken over a 55 gallon marine tank for the university and It was once a pretty tank. I have do monthly water changes, clean the glass and try to move the sand to keep algea off sand but it just grows back. It covers the once coraline on the rocks and the sand and is very ugly. I was thinking that maybe a blenny of some sort might help a little but is there anything else I should try and do?

 

does your university use a rodi unit for their water?
I take care of the 500 gallon tank here at Penn State University, we have a slight gha problem but are fixing it... Can I have some general info on what your university uses for lights, water, bioload, anything else that you think could be helpful?

 

Im gonna try to get a pic tomm. The lights are not the best but they are pc coralife lighting two actinic bulbs and two daylights. Idk the watts. there is a very small cuc. Two 3 stripe damsils. The rock was brought from the beach and so ws the sand. Theres where I think on of the problems is. It is beach sand and I dont know that much about that sand because I have never worked with it before. There is two good powerheads about 300 each and a 3 stage 100 galllon rated hob filter. I think the skimmer a cheaper skimmer but it skims pretty good. And the temp stays costant at 77.

 

well the number one thing i would say could be the type of water used for water changes... if they use tap water then it is constantly introducing new phosphates into the water and fueling the algae.

If it is rodi water used then I have some more ideas as to what it may be but water source is always the number one cause!