| First, fill a clean bucket with your source water. Test the pH when you first fill it and again after 24 hours. There may be something in the water which leaves once the water is not under pressure, altering the pH. This usually is the reverse of your situation... compressed CO2 lowering the pH coming out of the tap, with pH rising after a few hours. But it can also be carbonates in solution that settle out when not under pressure.
If the pH is stable in the test pail after 24 hours, then there is something occurring in the pond. My guess would be like Larry's & Russell's.... test the alkalinity of your source water. I'd guess it is low. The natural biofiltration process uses up what little there is, resulting in the pH shift. Be certain your pond is kept clean of debris. Leaves, mulm and such can greatly reduce pH in a low alkalinity situation.
Let us know what the alkalinity test shows. Then we may be able to do better than guess. |