after 3 months fish dying

Question
I have a small appproximately 75 gallon outdoor pond, I have worked and worked and worked, it got to the time I put fish in, I bought regular gold fish, and two koi, I had about 24 total fish, now three months later, goldfish are dying, I have a pondmaster 190, and also I have a waterfall, so i figured that the oxygen was ok.
Every other day, i find goldfish floating, the others that are left, are at the bottom, very sluggish, not responding to feedings,
the temp here has dropped, I live in east tennessee, temp has dropped into the high 40 or low 50 nice during the day. PLEASE HELP

Answer
Your pond is super overcrowded.  Have you tested the pH, ammonia, and nitrite levels? I'm guessing the ammonia is toxic.  A 75 gallon pond is large enough for a few (less than 6) goldfish.  Koi need a pond over 1000 gallons.  Koi grow to 3 feet long and goldfish grow to 1.5 feet long.  I've had many 14" goldfish that wouldn't be able to survive in a 75 gallon pond for long.  Until you have fewer fish, they will most likely continue to die.  To slow that, I suggest doing 10-40% water changes once or twice a week.  Be sure to add dechlorinator and some pond salt (I do a tablespoon per 5 gallons of aquarium salt in my tanks).  Test the water's pH, ammonia, and nitrite if not other things.  Put a mesh bag of fresh carbon and zeolite near the filter (near flowing water) to help remove impurities and extra ammonia.  Change that every few weeks, perhaps more.  As it gets cooler, the low oxygen levels of an overcrowded pond will become less of a problem but, when the pond freezes, the oxygen levels will again go down.  The best thing you can do is get some of those fish out of there and into another pond or aquarium.  You may want to add something like MelaFix as a general tonic but I'm not sure if they are suffering from parasites, bacteria, funguses, viruses, etc. so much as poor water quality and stress from being overcrowded.  I hope you can find a solution!  Good luck!

Robyn
fishpondinfo.com