Well, they both do the same thing, but the GHA might choke out the chaeto. When I set up my fuge, I had the same problem. I also got red slime in the fuge. I added a small power head and it helped tremendously. Some people dose iron to promote chaeto growth, but I would think it would promote GHA growth as well. For what it's worth, it took months for my fuge to really take off. Don't know why. Many people have had instant success. Oh yeah. I also keep snails in the fuge. Don't really know if it's helping or not.