I will weight in on this topic of biomedia vs. GDA. I have a 75 gallon AGA that had a fuval 305 running on it. The seal on the canister stopped sealing. This gave me a good reason to put together the sump that I have wanted to for awhile. It took me two months before I got everything together, tested and running correctly. In that time the tank got really bad algae all over the glass. You could barely see through it. I got the sump running and told myself that I would clean up the tank the following weekend. Well as the week went by I started to notice that the glass was getting cleaner. So I let it go for another week. Guess what? There is almost no trace of algae on the glass at all.
Now I don't think that the two Ottos I have in there all of a sudden got really hungry and went to town.
The only thing I could think of was the increased flow and addition of biomedia is what caused the algae to die off and the glass to clear up.