You have very low kH, which buffers stabalizes your pH and probably have an elevated level of CO2 in your tap water, which causes it to be low when it comes out of your tap. As it sits overnight the CO2 "gases out" and the pH rises. Not a big deal. I wouldn't worry about it unless you decide to get fish that like a really really acidic water. Most fish will do fine in the water parameters you describe. And if you're like the rest of us nuts, you'll probably eventually go crazy and want to add CO2 to your tank and the pH will come down again. Once again, don't worry about it....my kH is 2 as well and it'll be ok.
Len
Len
