Well, i have a 26 gallon bowfront that has some 4 guppies and 5 cories in it. I had platies, but i lost all 3 and some guppies to columnaris. So since i lost a majority of my fish, i'm thinking about possibly rehoming the remaining guppies and cories and restarting. So first of all, do i have to sanitize the tank before adding different fish? And if so, how do i go about doing that? My next question is about the stocking for it. Its a 26 gallon bowfront. I really want some sort of shell-dweller and was looking at maybe having a single calvus to help with the fry. Would that work? Also, what would be some fish that would fill in the upper regions of the tank? Thanks.