Used to keep Japanese Koi for 3 years in 2000. My pond was 7x5x6ft (depth). Please never guessing your water parameters.

To have healthy fish below are good water parameters:

1. Carbonate Hardness (KH) > 6 dH to maintain alkalinity of water to avoid pH crash which will kill fish immediately

2. Ammonia must be 0 ppm

3. Nitrite must be 0 ppm

4. Nitrate < 80 ppm

I do feel that Carbonate Hardness is the most important. Most of the time people say their fish die when they change water. This is due to very
low carbonate hardness. When new water is introduced (our tap water has low KH), pH will drop suddenly. (0.5 pH drop will stop fish gill to function and
fish cannot breath). Other than that, somehow KH affects your biological filter effectiveness.

Go buy water parameter measurement kits and learn how to adjust parameters if found out of above requirement.... most people buy pH measurement drops. They
don't even know what to do if pH is not 7..

After I learned all these, my water quality become better and the fish flourish.. Just my 2 cents... (later is somebody interested, we can learn advanced techniques... PP bomb)

If your biological filter is working well. Add a UV light (sold in most koi shop) to kill/sterilize algae... I installed the UV light
right after my pump in those days..

OR advanced method that I did lotsa time with great success, PP bomb but very2 dangerous and you have to know what you doing.
Potassium Permanganate treatment with Hydrogen Peroxide... water will be fresh like rain water and fish appetite will go crazy... not
to mention their color... It is a very dangerous, several hobbyists kill their fish so do your research b4 trying...

This post has been edited by Masculine: Nov 4 2010, 06:33 AM