I've been researching best species of loach to eat small snails which are damaging my Aponogeton leaves. I've had conflicting advice from several shops about how big different species will get and how aggressive they can be. I ended up finding the www.loaches.com site which I found very helpful - made me go for Botia striata rather than the Pakistan loach which was recommended by one shop - I understand these can get big and antisocial eventually. The B. striata have attacked the snails in a very businesslike way in a couple of days and seem very well behaved.