Exactly, they will add to the bio load, the only thing theyll do is maybe clean your substrate a little by consuming uneaten food or fish waste. Either way like any fish they give off ammonia! You can find em in creeks and rivers tooThey aren't filters.. they are filter feeders. They are a living organism and as such they work the same as any other living (animal not plant) thing in an aquarium, they eat and produce waste.
#1 S. Vettel