So, I began in a bad place, I guess. Someone gave me a 30L biorb. I'd read all of the negative reviews and cautionary tales about these tanks and so very very VERY carefully followed the set up instructions. These tanks are so small that really only tiny fish can live in them. I only had the tank running for 48 hours before introducing the fish but the kit came with some sort of bio stuff that is supposed to make the new tank safe for the fish. So it said. The fish guy said the tank should be okay, too. I bought six tiny gold gourami that the fish guy said should be okay in a 30 L tank. I floated their bag for a loooong time. He'd said they were okay with hard water and cold water but I think maybe the dude was underinformed. Anyway, they lived about two hours. Seriously! I feel terrible! Clearly I put them into a toxic environment. I'm going to buy the test kits and thermometers before introducing new fish but need some advice as to how to 'clean' a tank that fish have died in, how to set it up again and anything else. I've been reading the advice on the forums and I understand now that I should have only introduced one or two fish at a time, thought these fish died so quickly I think the water was toxic. What else could it be. I don't want to put any more living creatures in there until I'm sure it is safe. Any help would be appreciated.