Midwest Pond and Koi Society - Q&A #127

We have a 12 month old pond. 24 feet long 8 feet wide and approx 2 feet deep at one end going to 4 feet deep at the other holding approx 1500 gallons. We have a waterfall, pump and UV filter. The ponds get afternoon late afternoon and evening shade.

Approx 40 of the fish are about 6 inches long and the remaining 12 new ones are approx 3 - 4 inches long. Over the last 3 months (since the winter started) we have lost approximately 6 fish to ulcers in their sides and top of head. We were told it was because we left the pump on over the cold weather and therefore pushing cold water constantly to the bottom of the tank - this was stressing the fish. Since the warmer weather started we have treated the pump with an anti-bacterial treatment and also an anti-ulcer treatment. We have a lot of lilies so the fish do get shade from them but we have notices that during the past 3 weeks we have another 3 fish showing signs of ulcers. We feed some flake (Tetra flake) for the smaller fish and some pellets (also Tetra) for the larger fish. We also have a lot of blanket weed.

Do you have any suggestion as to what we can do or are doing wrong? We are getting very desperate now.

Hi Susan,

Ulcers are a secondary infection, usually found in stressed fish with either environmental or parasite-induced stressors.

If you have 1500 gallons and more than 40 fish longer than six inches, your problem is over-stocking. I notice that you haven't told me how you are filtering your water, nor what you water testing results are. Regardless, you need to cull back to about fifteen to twenty of your best fish, and find a way to unload the rest. The rule of thumb for koi is 100 gallons water per inch of koi, unless you have space-age filtering. I'd suggest you search on "water quality" and "filtration" on our website, and go from there.

We filter through a standard sponge box its capability is up to 2,000 ltrs. We lost 6 fish in 3 days all with signs of ulcers. None yesterday or this morning though thankfully. We did take some water to the garden centre where we bought the fish and they said the water tested OK. We did treat the pond on Saturday with Ulcer treatment and salt (we never used salt before). All our problems seems to have started with the hot weather. How do we get rid of parasites?

I will look on the web sites you suggested and thank you very much for your help.

Quite frankly, Susan, I'd not trust any tests but your own. Please read the Help File on water testing, and get your own test kit.

Your filter is mechanical only. If you are relying entirely on a small block of foam to remove ammonia produced by 40+ koi, you are truly deceiving yourself. You need to cull, and seriously upgrade your filtration.

There are a number of anti-parasite treatments available, all with very serious risks to your pond if mishandled. Please get in contact with a local club and get someone experienced out to look at your pond and fish. If nothing else, go to the AKCA website and look for southern Wisconsin resources.

The "anti-ulcer" treatment will not cure your fish. It alters some of the characteristics within your pond that favor the growth of Aeromonas, but this bacteria is an opportunist, and will cause ulcers only in sick, injured or stressed fish. It is actually an important component of the pond ecology, being the bug that breaks down the mucus that is a part of fish feces.

Salt is useful, but unless you are willing to push the concentration as high as 3 pounds per 100 gallons, you are not likely to affect the parasite load in your pond much. A "dip" of 2.5 lbs in 10 gallons might help individual fish, if heavily aerated. Make up the "dip", net out your sick fish, and, one at a time, place them in the high-concentration salt bath until they begin to tip. Pull them out immediately and return them to fresh water. This is a major stress, and may kill a seriously weakened fish.

Bob Passovoy
President
MPKS