thank you for your response, i dont think the down time in changing the res caused the problem since its a flood and drain also i have never had the problem before. hopfully they will recover and next change if i decide to try it again i will use .5 percent as you suggest...also my res says 30 gallons on it and i use 6 5 gallon buckets to fill it so im pretty sure, but yes its always good to cover the basics