Now, I've only been keeping fish for about 5 months, so based on my limited knowledge I'll give it a shot:
You could be overfeeding your fish to some degree and/or maybe too much light. You don't have any plants in your tank to compete with the algae, so the algae get to use up whatever nutrients are present and grow. I couldn't give an opinion on if your tank has good or bad algae, but if it's the good stuff... it's a simple "plant" and can benefit your tank a little. It can remove a tiny bit (there's not much algae) of the toxins in your tank, just as a normal plant would. Also, a free salad bar for your fish, if they like algae!
So, just my 2 cents.... anyone, please correct me if I'm wrong. Just my basic understanding of things. :)
Last edited by LeroyTheBetta; 05-17-2011 at 03:50 AM.