Ok I got this 130 gallon tank. It came with 2 aquaclear 500's. Junk I figure. Neways. I filled it up. Barebottom. Let it run with the old filters for about a week. Then I went to the river and caught about 25 or 30 minnows around 3 inches long and put them in there. All went well. I left them for about 2 weeks and put them in a buddies pond. Emptied the tank and it sit for a few weeks. Well me and my son went fishing and caught a couple small brighter colored blue gill and I set up a quick tank with a rubbermaid tote and one of the filters. No chemicals or nothing. Never tested the water I just figured if they make it then good deal. And they did fine for about 2 weeks so I bought 3 6 to 8 inch blue catfish to put with them and they did fine for about a week. So I went to wal mart and got some play sand and put it in the tank with some rocks and driftwood and filled it back up just like I did before the minnows. Let it settle for a couple hrs and put the fish n the tank and emptied the tote. About 2 hrs after that I go downstairs and the tank is leaking from somewhere. So I setup the tote again the same way I did for the bluegill the first time. Now everything is dead. I mean they died quick. I dunno if the sand poisoned them or what happened. I'm new to this hobby and that way just like wow. I'm glad it wasn't some expensive fish. Ne ideas on what might have happened? also is sand not suitable for fresh water setups. I've seen it before but I dunno why mine failed