Malaysian Trumpet Snails

Often regarded as a pest snails, MTS are far from that. They look cool and stay small making for an excellent tankmate for basically all fish! They even eat algae. They generally don't need many supplements. The thing about these guys is that they only reproduce to the limits the tank can hold. If they make 100 babies and there is only feed for 10 then the 90 will die very early. If you have a large quantity for a smaller tank they can act as a signal for when there is excessive waste. 

They also arate the substrate as they burrow and shift it around over time, helping reduce dead spaces. 

The snails only generally grow to about a few cm in length

They are very easy to maintain and basically everyone of my tanks have them for all those benefits.