I have a 600 gal. formal pond. Last time I added water (30 percent water change) my ammonia got really high (3 plus) and my 2 small koi died. My 2 Comets and 2 shibukin were fine. Yes, I used dechlorinator. I need to add water again (due to evaporation from the heat,) and am very tentative. I have replaced the koi (again they are small, less then 6 inches each.) I tested the tap water I use to add and the results are : PH 9, Ammonia 1, Nitrite .25, and phosphates .5. I have left a message with the water company to find out if they use chlorine or chloramines in the water, am awaiting a response, but my decholinator covers both.

My thought is to add the water & dechlorinator then immediately test for ammonia (the fish were a good indicator that something was up last time) & take care of that accordingly. Any other ideas/thoughts? Does that fact that I am dealing with a huge algae bloom at the moment have any bearing on this?

Thanks!