[sir_keith]

... I really don't want to have to give them up ...

It seems to me that if you want to keep the Aphanius- which are seriously cool fishes IMO- the simplest solution wold be to re-home some of the shell dwellers. It sounds like you have an excess of males anyway. Good luck. :fish:

 

[sir_keith]

Is there any way to tell the sex of the shelldwellers? They all look the same except some are a darker color than others.

Difficult when they are young, but eventually the males grow larger than the females.