I agree with drblakjak55. When I first saw your set up, the first thing that came to mind was that your aquascape was really dense with no pass through or tunnels for water flow. IMO this is a trap for ditritus to build which would cause algae and the likes. There are many good opinions the have been provided but what i would personnally do is the water change as suggested but first do a re-acquscape of your rocks that will provide lots of pass through area to allow flow. i would not bleach the rocks due to it already having too many good bacteria. Obtain a powerhead or two (those can be inexpensive) that is adequate for your size tank and I do believe that would be a good start. Patience is the way to go so take things slow. Just have fun with it and embrace the challenge.