Fluctuating pH

[Banafish]

Carbon Dioxide (CO2) and other gasses (nitrogen and oxygen) should stabilise in water within about 24 hours, sooner if the water is aerated. The fact the pH continues to change after a few days to a week would suggest something weird is going on.

You could buy a CO2 and O2 test kit from a pet shop and test the water. The shop will probably have to order the kits in for you but they are available and you could check the levels to see if they are affecting the water.

Ok, what else should I do in the meantime?

I will see if the shop has a CO2 and O2 test kit.

 

[Colin_T]

Maybe increase the aeration/ surface turbulence in the aquarium and see if that makes a difference.

Take your test kits to a pet shop along with a sample of the tank and river water and get them to test it. You should test it with your kits too and compare the results. If the results are different, one of the test kits is stuffed.

Outside of that, the only other thing I can suggest is contacting a lab and have them do a complete test of the river water to see if there is anything unusual in it.