Looking for some help, have a 60 gallon tank that once was used as a fresh water tank. My API test kits are show perfect water with .25 on ammonia. My fish are doing great the tank is been up and running for 7 months. I can not get inverts to last more then a day or two. 6-8 fish nothing big, few clowns yellow eye tang, few other don't know the names. Any ideas??