ph water change

Question
I have had a tank going for about two months. every week as water evaporates i take a little out and replace about 10 to 15 percent. last week i took a little more out as was suggested every couple of months. about an hour after the change my fish started acting wierd and by the morning i had three catfish left wich are still alive. My ph is off of the charts high. i am scared to get it down and have it happen again. How do i get the ph down and how do i avoid having it happen again. I also dont understand why this time the water change did this when it was fine every time i did this before.

Answer
Hi Brian,

PH can increase due to a substrate which has a carbonate in it.  If the acidic water and carbonate react, raising PH.

Ammonia can cause a rise in PH as well.  Please try using Zeolyte crystals and putting them in a net, introducing them to a moving stream, perhaps inside the filter.

Are you using tap water?  I do not recommend that.  But, if you do, please use a dechlorinator, as it will kill your fish to use tap water as well.  Even well water is treated with Chloramine, by law.

I hope this has been helpful.  It was in our question pool for quite some time and today, someone has referred it to me to personally answer.  

Got it today, and as usual, I'm on it. :)

Thanks,
Renee