Yeah, I agree. You already have quiet a few fish in your tank. I think that the best bottom feeder would be a gravel vac. I use some stuff called "Phosguard" by Seachem in my tank. I put some in a filter bag and stick it in one of the compartments of my Fluval. It lasts for like 3 months. It absorbs the phosphates in the water (which is what algae feeds on) so there is a significantly less amount of algae growth. And with thoes fish, you won't be able to have live plants, so you won't need to have strong lighting. I have virtually no algae growth in my Oscar tank. My Oscar lives with 5 giant danios in his 75 gallon tank. I never really found a bottom feeder that worked (or any other tankmate, so I gave up). My Oscar picked on everything. You would have to get something rather large so it wouldn't get picked on, and then you are really going to be overcrowding you tank.
This is just what I have learned from my Oscar experience, hope it helps.