Why does my pH climb during the day?

“So I noticed my pond starts at a ph of 7.8…with shade and gradually goes up to 8.6 to 8.7..eventually gets full sun…then goes back down…and back in shade.  I have been told that since it’s gradual climb up its ok for the fish.  In your opinion is this true…I was thinking of adding a shade cloth or pergola to keep it more steady. “


Most pond fish don’t care about that *change* in pH.

Besides that, fish can INCREASE their pH pretty much as fast as they want and it doesn’t matter. It’s a rapid *decline* of MORE than a point that can matter. And even then, as long as it’s in a happy range it doesn’t matter. LIKE 8.3 dropping back to 7.

The kicker, is dropping from 7.5 right down to 6. That hurts.

The reason for that rise in pH during the day is the ebb and flow of carbon dioxide.

During the evening, plants are producing carbon dioxide and through the night which makes carbonic acid which brings the pH down.

During the day the plants use all the carbon dioxide, which removes carbonic acid from the equation. And that’s the pH climbs..

Author: Dr. Erik Johnson
Dr. Erik Johnson is the author of several texts on companion animal and fish health. Johnson Veterinary Services has been operating in Marietta, GA since 1996. Dr Johnson graduated from the University of Georgia College of Veterinary Medicine in 1991. Dr Johnson has lived in Marietta Georgia since 1976.