Do Decorations Raise PH?

[Murphy]

Being a semi-new Betta owner, I have a question to pose to anyone that might have an answer.
I have been keeping my Betta in a bowl since "adopting" him. I now have set up a 2.5 gallon tank to transfer him to. I filled my jugs with water and conditioned for an about 2 days. I checked the PH level before I put the water into the tank. (It read almost exactly 7.0) I filled the tank which contains gravel, some silk plants, a stone tunnel, and an air stone. I have a foam bio-filter in the tank.
Well, after seeding the tank and letting it sit for a week, I again rechecked the PH level and it was at the top end of the scale!
My question to all of you Betta mavens, is; is there anything in the tank that will raise the PH level that much? I don't really want to have to add that much PH down and burn the little guy.
Any suggestions/solutions?
Thanks

[amanichen]

Yes, tank decorations can raise the pH. Usually this will come from natural stone, especially any which contains lime (calcium carbonte.)

You should also realize that ammonia raises the pH of water, and monitor your ammonia level. If the ammonia level is high, then chances are the pH is also high.

A third thing to look out for is the effect of dissolved CO2 in your water. Compare a sample of 24 hour old water, with one that's been freshly drawn. Carbon dioxide temporarily lowers the pH of your tap water, and after it is drawn, the CO2 outgases and the pH goes upward.