If you notice your fish look like they have a white haze on their skin or that their skin is peeling...test for pH and do an immediate 50% water change before going any further.
Think of pH as the way the water feels against the fishs skin. A low pH burns the skin because it is acidic. High pH chaps the skin because it is alkalinic. The ideal pH reading for koi and goldfish is around 7.5 but these fish can tolerate a range between 6.8 - 8.2.
We prefer to use pH strips to test pond water because it not only does it give you the pH level it also indicates whether the water is buffered properly or not. Buffered water means the pH is stable.
pH tests vary a few points at different times of the day. It tends to run higher at night then lower by morning, taking its cue from the natural CO2 and Oxygen exchange of the plants in the water. The difference in the pH at different times of the day is called pH swing. When it is more than just a couple of points off it can be dangerous and unpredictable. The object is to stabilize the pH at an acceptable level.
Now think of the pH suddenly falling. It would feel sort of like being dropped into a vat of acid. When the pH suddenly falls to a 6.5 or below it is called a pH crash and is very deadly. Fish subjected to a mild pH crash suffer peeling of the skin, very similar to our sun-burned skin peeling off. Weve seen cases of the jelly caps of fancy Orandas literally eaten away. Sever crashes can end with complete fish loss. In the case of an emergency a water change is in order or take the pH up quickly. A very clean system with little organics tends to be lower in pH. Bead filters, because of their efficiency, can actually contribute to low pH readings. For readings that tend to stay low, baking soda in small quantities can be used to bring the pH up but you do not want to raise the pH quickly unless its an emergency because it can shock the fish. Instead, its best to use carefully prescribed products designed to raise the pH over a period of time and hold it at the desired level. We use pH stabilizers with great results. Its important to know that the stabilizers must be added back whenever water changes are made.
Concrete leaching into the water will cause high pH readings. Newer ponds where stones have been concreted together in a stream or waterfall often see readings close to 10.0. Common household products can be used to bring down the pH. Again, care must be given to bring it down slowly. Well be glad to help you determine how much of what product to use for your unique situation. Once it is down youll then stabilize it with pH stabilizers.
Aquariums and ponds are not immune to pH swings and crashes. Its a great idea to test in the morning and in the evening for a week to get an idea of the severity of any swings in the readings. The pH changes in a small container making it impossible for us to properly test your water at our facility. Its best if you take home the test strips and perform the tests from your ponds side.
If you find that your pond is subject to pH swings there are some very simple (and not really pricey) things you can do to lower, raise and buffer your water. Testing is the key and stabilizers are the answers.
From The Fish Health Edition
of What's Up, Doc?, April, 2000
© Copyright 2000, The Pond Doc's Water Garden Center. All rights Reserved. Reproduction of this article prohibited without prior consent of The Pond Doc.
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