scubadoo, it sounds like your tank has cycled. The ammonia may have been too much but hard to tell. I would suggest doing a large water change, maybe 75 to 90 percent, just as you would when the cycle is finished. Then add enough ammonia to raise the level to about 4 ppm and see how long it takes for the ammonia and nitrite to drop back to 0. If it happens in about 10 to 12 hours, you're ready for fish.