The first thing you need to do is check you water quality. You want zero Ammonia & Nitrite and very low Nitrate (less than 50ppm idealy) If you have measurable quantities of Ammonia and Nitrite (0.25ppm or less) increase oxygoen and add some bacterial cultures such as Kusuri Filter Boost. You should turn off your UV to help speed up the bacteria reproductive process too.
If your ammonia/Nitrite levels are higher than 0.25ppm I would suggest you try and buy some Ammolock which you can add to the pond to lock up the ammonia and stop it being toxic to your fish. If you have levels of 0.5 upwards, Partial water changes using dechlorinated tap water are necessary. You can also try adding some Zeolite to your filters which will help soak up some of the excess ammonia and if Nitrite levels are high, add some salt to the pond to raise the salinity to 0.3% over a three day period (0.1% per day). This will help protect the fish from Nitrite. Use proper pond salt to do this and disolve it completely in water before adding it to the pond. Salt crystals burn if they come into contact with the Koi!
There is no easy and quick way to get your filters up to speed. If they are new or simply slow to come out of the winter slumber, all you can do is nurse the pond and fish through until the filters are working properly.
Water Changes: NEVER use tap water, dechlorinated or purified to clean filters. This kills off the bacteria you are trying to encourage. Just use pond water. You should not need to clean a well designed biological filter, just the vortex and perhaps the static K1 chamber if it is intended as a mechanical stage.
Re Ulcers: Find a local Koi keeper who can have a look at your fish. You may well need to give your Koi antibiotics and the best way is to inject for which you need expert help. I won't pretend that things are not quite bad if you have ulcers because thdey are. This is a clear sign that the fish are having a very difficult time of it and unless you take action quickly they will not survive.
Best of luck.
Alan F.
Posted on Apr 29, 2007, 1:20 PM from IP address 213.120.101.21