Nice tank! You'd probably be fine with a school of small tetras or rasboras as fishorama said. Cherry shrimp would also do fine if you don't mine losing them periodically to the rams, especially the babies. Shrimp are very low bio load. If you get some additional plants to create good hiding spots for the shrimp (java moss makes a really good shrimp nursery) and start with 20 or so cherry shrimp they might breed quickly enough to maintain a population, and help keep your rams fed at the same time.