Dubethenewb, just keep testing and watch it, worse come to worse do a water change. I would wait at least two if not 3 days before you dose again, change water, or test. Let your water settle with what you have added. I am confused now... How are you getting that 15 1/2 tsp = 2 tsp? 15 1/2 tsp = 7.5 tsp into 8oz would be about double (a little less) than the recommended amount.