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Koi Pond Water Changes

Water ChangesPond water changes are simply the removal of some old pond water, and the replacement of that old pond 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 pond water changes, at all. Thirdly, failure to do pond water changes allows the accumulation of background pollution such as phosphates and proteins which inhibit koi health and growth. Finally, pond water changes need to replenish trace elements and minerals in the water which koi and the bacteria in your pond filter need to thrive.


Chlorinated and chloraminated 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 your pond pond slowly WILL dissipate a lot of chlorine, but will it dissipate all of it? Dechlorinate . By dechlorinating the water, you can be 100% sure the chlorine is gone and will not harm your koi. 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) pond filtration system. However, if your filter is new and/or you are doing more than a 50% water change I would recommend a dechlorinator that would also remove ammonia such as Dechlor & More.  

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

"Topping Off" your koi pond is not a water change. You should know this about pond water: The solids in your pond 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 your koi pond and accumulate over time. As koi pond water level goes down by evaporation, you may notice that your koi perk up as you add water back. There is a transient increase in pond 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 your pond water over time. Real pond water changes should be endeavored.

Ideal water change regimens

Every week 10 percent water change
OR: Every two weeks 20 percent water change
OR: 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 your koi pond. You will notice a real boost to your koi health and growth.

Major water change: Simply drain your koi pond down 60-70% and add dechlorinator. Then refill your koi pond. Don't do this in the PEAK of the summer as you might chill your koi (I've never hesitated, but that's just me). 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 pond water changes, you should have robust, hungry and healthy koi. Koi may still become ill, of course, however it is much less common in well managed koi ponds with LOTS of FRESH Water. Fact is, if you wouldn't swim in in your koi pond, your koi shouldn't be.