You don’t want to mess with it a lot. Some people try to move it around, up and down, but pH is logarithmic so any change, sudden change, that’s even a half of a point up or down could be really dangerous to your fish. What you do is boost the alkalinity in your water, and a lot of times people confuse alkalinity with a high pH, but actually a high pH is a basic — above 7 is basic, below 7 is acidic.  When you boost the alkalinity, you’re actually buffering the changes in the pH, so you use products like water conditioners and stress coats which boost alkalinity. A simple thing like sodium bicarbonate (baking soda) buffers by boosting alkalinity. So you want to avoid drastic changes in pH.

What pH levels do fish thrive in?

They thrive in 6 to 8. The ideal pH is 7.5. The most stable pH Koi can thrive at consistently is between 6.8 and 8.2.  PH below 7 is acidic which burns their skin, and a high pH will chaff their skin. A variation more than .5 in a 24 hour period is very dangerous and that would be considered a pH swing.

Are there any other symptoms that fish will display that tell you there is a pH problem or a water problem?

No, not so much. If pH is higher than 7.5 and you have any ammonia readings in your pond — you know you can get ammonia from over-stocking your fish or having too many fish in a pond — so if there’s any ammonia,  they can tolerate a little bit, but the higher the pH, the more dangerous the ammonia is, so it becomes more deadly to them.

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