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So, we know that the high pH is caused by something in the pond, which is concrete and less than one year old. Seems likely it is the concrete leaching, but if there are any other alkaline materials in the pond (such as coral-based rock around edges, limestone used for decorative purposes in a waterfall, etc.), they could be a contributing source of high pH. If those possibilities are ruled out, you are left with how to address the high pH without removing the koi. I do not believe there is a quick solution, but I do have a simple one to suggest. But first, remember what I said above about avoiding pH fluctuations. You do not want to subject the koi to unstable conditions. It would be better to continue current practices and simply endure the high pH than have the fish subjected to large pH swings.
The leaching will reduce over time as the more soluble components of the concrete surface dissolve into the water column. The lower the pH of the water in contact with the surface of the concrete, the quicker neutralization of the surface will occur. (Note: It may never be truly "neutral". There may well be a continuing tendency to increase pH for many years, but at at a decreasing rate.) Also, soft water will speed the process, but too complex and impractical to address in your friend's situation. Once a thick growth of algae becomes established on the pond walls, there will likely be less effect on pH. You could use an acid additive, but you would need to be very careful and precise. The pH would need to be tested frequently and on a regular schedule every day (and night), with dosing in small quantities occurring on an almost continuous basis to prevent pH bounce. I do not believe it is practical.
So, that leaves water changes using the moderate pH source water. I personally believe in large water changes on as frequent a schedule as one can do them as part of a regular maintenance program, but large water changes would not be advisable in your situation. ... at least at first. I'd suggest trying daily 5% water changes. After a couple of weeks increase to 10% daily water changes. If this is too frequent due to work/lack of time, then do the water changes on alternate days. The important thing is to do them on a regular schedule and for them not to be so large that the koi have to endure a lot of fluctuation. (Dechlorinator is cheap, so use it.) Suggestion: Conduct a test by placing 2 gallons of the high pH pond water in a large container, and add 1 gallon of the source water. Measure the pH immediately. Then measure pH again in 5-6 hours. This will indicate the extent of pH fluctuation doing a 30% water change. If the first reading lowers the pH by more than 0.5 (some would say 0.2) you cannot change so much. If the second reading shows the pH rising to be close to the original pH in just 5 hours, then you know that there is a high buffering capacity in the pond water that will cause pH bounce, so you will want to limit the size of the water changes so that no more than a 0.2 pH differential occurs between completion of the water change and 5 hours later. There are many who would disagree with subjecting koi to a 0.5 pH shift during a water change. I would not do it to my own koi. Nonetheless, assuming the replacement water is introduced over a period of 2 hours or more, I believe it will be O.K.[BUT ABSOLUTELY NOT ANY MORE THAN THAT], but not if the koi will be re-subjected to a pH increase of more than 0.2 in the 5 hours following. ( I view this as maximum fluctuation limits, not desirable ranges.) Try testing different water change percentages in the container until you find the size of water change that stays within these limits. In your friend's pond, it may be that no more than 5% or 10% can ever be changed without subjecting the koi to too much fluctuation. The goal is to gradually increase the rate of water changes until the leaching from the concrete is balanced out at a pH level deemed acceptable. It may take months, but I expect over a period of 3 months it will reach a stable point, if not sooner. If this sounds like too much work, then do not start a process that won't be followed through. Good luck.
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05-05-2004
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