Hi I'm Barb and I need some advice. Got a 75 gal tank with cabinet from friend who had saltwater. The tank was precut and all the plumbing was in place. All we had to buy was things to build the sump. So it's a 20 gallon long tank. The first section on the left has the inlet tube that flows right into a sock filter, next two sections are small for the flow over and under, the third section is wide and and the last sectiion is wide for the sump pump which pumps the water back up into the tank. I transferred my old fish from their 40 gallon breeder and even after growing benefecial bacteria using ceramic cylinders in the first section with the sock, I killed all my fish including my 2 seven year old parrotheads. So I cleaned out the whole tank and started over again. Since then I have killed about 10 more fish. The only problem I saw--- was in the first section that houses the sock and ceramic cylinders. It had a heavy thick layer of scum floating on the top the water. I don't know what it was or why it was there. Since the last killing, I cleaned out and emptied the whole system and my new fish are in a 10 gallon tank and they are NOT HAPPY !! I had planned one section to grow plants but not sure exactly how to set that up. Since then, I got about two gallons of bioballs and I'm not sure where to put them. I think they work better when you have some kind of trickle system running over them but not sure how to do that either. Someone else told me that the bottom tank should have a top on it and I don't know if it should be sealed lilke that. I also have sand in the top tank because it was mostly for my parrotheads. Now I got 4 baby parrotheads and goldfish in my 10 gal. tank. I've already spend almost $400 dollars on this tank and I'm going broke. Any thoughts are greatly appreciated.