I have a back yard pond, about 300 gal. It is filtered 24/7 and has top water flow. I clean the bottom of the pond every year and have never had a sick fish. I have 15 fish, 2 koi and 13 gold fish. 2 of the gold fish are swelling up, at first we thought the were pregnant, but 1 of them is about to explode. the scales stick out. I guess it is dropsy, but in 4 years this is the 1st time any fish have gotten sick. The fish stay in the pond year round. Is there anything that I can do for these fish?