Any spike in ammonia can cause serious problems...definitely look at a significient sized water change. I'd even do daily changes of 20% or so until it becomes stable again...plus there are a few products designed to reduce/eliminate the adverse effects of ammonia. If I had much livestock I'd look at using some sort of chemical to lock-up the ammonia until things returned to normal.Plus if you have a well established filtration system it should be able to handle a mini-cycle quick enough to prevent serious losses....best of luck....I'd hate to experience the same situation. nmreef@cox.net