Eh... I don't think there is a sole purpose for anything in an aquarium. Just like in nature, most living things are part of a cyclical system that benefits the whole system by doing its parts. Inverts like tubifex worms are the bottom of the food chain (provided a predator is present), and they also offer the benefit of breaking down waste for plants and aerating the substrate. MTS do the same thing, but will not have predators in my set-up, so they won't serve as a food source in this case. I'll have some MTS in the tank too simply because I like them and they are beneficial to the tank with or without a predator.
That said, tubifex worms must have a natural ability to hide somehow or they would be extinct by now with all the fish out there in the world looking to make them into lunch. My fish tell me tubifex taste like Nutella, so I can see why they would be interested in them. I'd like to have some in there to increase the level of naturalness (if that's even a word) I can mimic in a glass contained body of water. If I expect for them to survive "in the wild" environment of my aquarium, I'm going to have to provide them with some "rocks to hide under". FIRST, I need to get my hands on some. Anybody got a source for me?
