Strange PH Issues
I am having a strange issue with pH. Our kids won some goldfish at a fair a few months ago. So, we got a 10 gallon tank from a family member, a marineland penguin 150 filter, and put the fish in. No issues! Yay! Time goes on, the fish get WAY too big for a 10 gallon tank. Time to upgrade. So we go and purchase a 60 gallon tank, two marineland penguin 350's, and fill the tank up with filtered, sofened water. Tested the pH before and after placing the fish in the tank, all is well. 24 hours later, we tested the pH and all was still well. Sitting at dinner we noticed the fish acting a little strange. SO we tested the water again....pH was up from about 7.5 to 8.8. AHHHH!!!!! Luckly we kept the 10 gallon tank prepped and ready just in case. We got the fish out and put them back in the 10 gallon tank, which was still in the 7.5 area. Weirdest thing, a few hours later while trying to figure out how to tune up the new tank we tested the pH again....same as the other tank now. What in the world?! What would cause the pH to fly up to 8.8 in 10 hours, and then cause it to go back down to 7.5 in a couple of hours?!
Any advice would be appreciated. It would really suck to kill the poor fish because I'm a moron.