Hey everyone, after having to re-register, I'm finally back... I wanted to let you know about the saga I went through with my tap water while I was away, in case it helps anyone else...

I've got a fairly new tank that just started to cycle. The pH is always around 7.8 to 8.0, which is what the tap water is where I live, based on testing the tank before I added any fish or anything in the very beginning. Ammonia went up a little, so I wanted to do a small 10% water change one morning... so I took water out, filled a bucket in my bathtub, added dechlorinator, swished it around, and poured the water in. My fish freaked, and I thought it was just because the water changing process was new to them. But they continued to stay in hiding, looking stressed. I checked my pH, and it was 7.6, down from 8.0 the evening before! I checked my tap water, and it was 7.2. I was puzzled, and not having you guys, I went to fishgeeks.com, where someone mentioned water companies sometimes dissolve lots of carbon dioxide in the water. I guess it helps prevent build-up in the pipes. But CO2 also makes carbonic acid, making the pH go down. So she told me to let the water sit for a while, to let some of the CO2 escape, and test again... and after 12 hours, it was about 7.7, good enough to do another water change.

I hear about all kinds of stuff that's added to tap water, but I haven't read about this anywhere on fish websites! Does everyone know about this and I'm just out of the loop? Or could this be a helpful thing to tell people to watch out for? I'm only doing water changes with aged water from now on, of course. Good thing I have a small tank, I don't know what I'd do with a bigger one.

It is strange what some water departments do to the water. Mine comes out of the tap at almost 10!!, with strangely almost no KH, so by the time it sits a day in my garbage container, it is down to probably 6.5, which of course is no use either. So I had to compensate with crushed coral to have it on a decent 7.2 in the tanks.
I am moving tomorrow, and I just wonder what new strange things I find with our new water. I am an optimist and hope its gonna be better!!
I am so glad your fish made it through okay, I have seen fish just almost instantly die from ph crashes...

CO2 is added to hard water to remove calcium (precipitate it as calcium carbonate). Water oversaturated with CO2 will increase its pH as it equilibrates with the atmosphere. It is just the opposite of ground water supplies which have a CO2 defficiency and come out with high pH... when it equilibrates with the atmosphere the pH will decrease.

Ah, ok, that makes sense. I had no clue.

OK, Kingyo - I have one for you. We just had rain - after having NONE for what seems like forever. And, of course it was not just rain, it was RAIN!. My well water comes out at about 10 pH. Today it tested at 7.2 pH. Is this because I am reading rain water (acid rain?) and it will revert to the underground aquafer that we have been tapping or is this just a weird happenstance and I am reading too much into it? I have never tested the rain water. I will, when and if it ever rains again.

I suppose that if you are pumping water from an unconfined aquifer there was just some kind of dilution effect. The rainwater percolated into your well and mixed with the groundwater.

Yeah, I am pretty sure that is what it is. Dilution. For, today, the water is at 7.6. I am thinking that I am almost ready to say to heck with the well water and go 100% RO with additives. I had been using 5/1 combination of the two, but if the well is that unreliable..... (This is our new deep well. The old well is REALLY nasty).

I found a product at Goldfish Connection called "Trace Elements". There is also one at PetCo that is supposed to have all you need in it to add to RO water. Rather than collecting all sorts of stuff from around, is it possible these could do the job for me? Any one with any experience or knowledge on the subject?

(I am thinkng of putting in a substantially larger RO tank. But it is a substantially larger bill, and all the waste water needs to be properly used. Not a trivial job.)