Catfish are bottom eaters. Wouldn't they help clean up a bit of the stuff? With your tank size, I would not buy another fish to keep the balance. 1 gallon of water for 1 inch fish is the rule. Less fish..less waste..less pollution. Leave the rest for your filter to take care of. Also reduce the light and less aglae build up. Another thought...hard water promotes algae too. In the future, you might want to consider getting a larger tank since your are enjoying this hobby so much. The larger the tank the easier it is to maintain the balance too. I hope I could help you.
Theresa

Bettas eat shrimp, frozen,fresh, or dried. And catfish can be verry aggresive, we had a corry cat that liked to think he was the dominant fish in the tank. He would chase even the ciclids around. So when summer came we put him in the pond with the koi/commetts he would chase them around the 110 gallon pond so fast that we lost two of them too jumping out of the pond. He eventually met the same fate, we found him dried up on the ground. Try looking at snails or less agressive plecto.( not sure of the spelling) The catfish was only 3-4 inches and was definately very agressive.The koi/commetts were the same size. hope this helps. chris