1 dead fish

most of you know by now that we are the proud owners of a 28 gallon fish tank. it is home right now to 9 tropical fish, and rocks and some fake plants. well, we started out with 8 fish and one died at the begining of shabbos, i think it waited till after licht bentching so it was able to taste shabbos in our home before it went bye-bye. being that the fish store has a 14 day live policy ( if they die w/in 14 days we could return them) i took our dead little fish off the filter ( which was apparently powerful enough to suck it off the floor of the tank, and across the tank) and took him back to the store, where they put him in the fridge. i think they are waiting for technology to catch up to the time and they will revive him, but thats for a later time. while i was there i said i have all "non aggressive" fish can i also get a "semi aggressive" or will he beat up the others, they said he would eat the others, so then i said well i have 3 black molly fish and one of them keeps nipping at the others, so the lay at the store said oh he sounds aggressive i would take him out and put him in a nother tank, so i'm thinking hopefully the fish will toughen up against their new aggressor or they'll be killed within 14 days!
gut voch