How big is the pond Sorch? Is it something that you can bail down a bit? Is the fountain made of concrete that could leach lime? What is the pH of the water you used to fill it with in the first place? How high does the water temperature get? Do the fish have some area of shade they can retreat to in the heat of the day? Is the water you use chlorinated?

I killed some of mine the first year too because I cooked the poor little buggers when the water got too warm and I hadn't provided them with any shade. Also each of my tubs contain about 35 gallons of water and only will support 2-3 fish per tub. How many gallons of water are in your pond?