If you would not swim in your pond,
your fish shouldn't be either.

Water Changes Are Critically Important  

Water  changes are simply the removal of some old water, and the replacement  of that old water with new water. It sounds so simple but there are  problems, nationwide. First, water can be chlorinated. Second, a lot of  people don't do water changes, at all. Thirdly, failure to do water  changes allows the accumulation of background pollution such as  phosphates and proteins which inhibit fish health and growth. Finally,  water changes need to replenish trace elements and minerals in the water  which fish need

      Chlorinated water is usually supplied to hobbyists "at the tap"  from municipal water supplies. The water company adds these two  chemicals to disinfect the water. Each day, municipal source-water is  tested for eggs, spores, ova and cysts of various pathogens. If any are  found, it may be that the municipal water authority will double or  triple the chlorine or chloramine concentration. Spritzing the water  into the pond slowly WILL dissipate a lot of chlorine, but will it  dissipate all of it? 

    By dechlorinating the water, you can be 100% sure the chlorine is gone  and will not harm your fish. When your municipal water supply uses  Chloramine you will be relieved to know that dechlorinator can still  bind the harmful Chlorine. The remaining Ammonia should be no match for a  cycled (properly functioning, well colonized) filtration system. 

    In  speaking to people from across the country, I found that about forty  percent of the hobbyist are not doing ANY water changes at all. This  accounts for recurring illness among the fish, slow growth, and poor  color. This is the most common cause of the "seven inch, seven year old" Koi. A Koi in good water with plenty of water changes should grow at  least 3-4 inches per year. Hobbyists should be encouraged to follow a  water change regimen as outlined in the chart below.

"Topping  Off" the pond is not a water change. You should know this about water:  The solids in water do NOT evaporate, nor do many of the chemicals in  the water. This means that the nitrates, phosphates, a good bit of the  carbon dioxide, all the salt, minerals, etc NEVER leave the pond and  accumulate over time. As the pond water level goes down by evaporation,  you may notice that the fish perk up as you add water back. There is a  transient increase in water quality after the addition of "new" water  but it's rapidly offset by the dissolution of the existing background  pollution. So, "topping off" actually concentrates solids and organic  chemicals in the water over time. Real water changes should be done.

Ideal water change regimens

Every week: 10 percent water change

Every two weeks: 20 percent water change

Every three weeks: 30 percent water change

No  matter which of the above regimens you pick from above, I HIGHLY  recommend that twice to three times per year you should perform a 60-70%  water change to really REFRESH the pond. You will notice a real boost  to fish health and growth. No matter which of the above regimens you  pick from above, 

Major  water change: Simply drain the pond down 60-70% and add dechlorinator.  Then refill the pond. Don't do this in the PEAK of the summer as you  might chill the fish (I've never hesitated, but that's just me I slowly  add cold water to my ponds My KOI love to play in the shower). But  SURELY in the early summer and late summer you should find the fish VERY  appreciative of this service. 

If  you are performing the recommended water changes, you should have  robust, hungry, healthy, happy fish. Fish may still become ill, of  course, however it is less common in well managed ponds with LOTS of  FRESH Water.