I have a 30 gallon tank , over the back filter and air filtration , my prob is i have had my tank up bout 1 month or so when i started it i used start right, I decided to put a tiger oscar and a algae eater in there , well i got my first alage eatr from pet smart it died for days later , so i took a water sample and it back they told me my water and nitrates were all ok not enough to kill it, so i broke my tank down and cleaned it, and put start right in it again and put my fish back in well in a week or so the alage eatr died again , so i thought maybe it was just bad fish in the store so i took a water sample and everything was fine so this time i decided to go to another store and get a algae eater well it lived a week and 2 days and died , I have noticed before they all die the will turn brown or have a brown spot , i have tried all fish stores and nobody knows whats going on any help would greatly be appreciated.......