High tank pH, low tap pH, safe water changes?

[fishie111]

Yesterday, I discovered that I am having a problem with high pH compared to my tap water in at least one of my unfiltered betta tanks and my 10G cycled goldfish tank (the two 1.5 inch fantail goldies that live in it are moving to a 28G as soon as it is cycled and the 10G will become a betta tank).

The unfiltered betta tank is a 5 gallon hex- it has one male CT betta as its resident. I've stuck in some java moss and pennywort which both seem to be doing well. The betta is the tank's first resident and has only been in the tank for 7 days. He is due for a water change (though the NH3=0 and NO2=0, so it is not urgent). I did some pH tests last night and found out that the water in this tank has a pH of 8.0 and my tap water has a pH of 7.2! I'm now afraid of doing a 100% water change because of the extreme difference in pH between my water and his tank.

Besides the plants and a resin rock ornament with a silk plant attached to it, there is no decor in the tank- it is bare-bottom. I treated the water I used to fill it with AquaSafe and added some aquarium salt. I also have Amquel+ and Novaqua+, but I have not used them in this tank.

I was planning to put a filter on this tank- I have had some media for it in my cycled 10G about a week that I planned to use to seed the cycle. I was planning to move the betta to another tank so I could do a fishless cycle- but at the moment, I don't have any place to move him to. I could cycle it with him in it, but it does make me nervous, however, maybe this is the best way to minimize the stress of the pH variation since I could do smaller water changes.

The 5G currently has NH3 = 0 and NO2 = 0, I treated the tap water with AquaSafe when I filled it.

I'm also worried about my 1G and 2.5G betta containers and their 100% changes, though I have not yet checked their pH to see if they will have the same problem.

I'm less worried about the 10G since I only need to do partial changes on it- probably no more than 25% per week, but I still wonder what is going on. The 10G houses two 1.5 inch fantail goldfish. It does have gravel in it- natural colored river pebbles- that I bought at Walmart. The only other decor it has are 2 plastic plants. Since goldies are messy fish, I use Amquel+ to condition the water during changes.

Any ideas as to what is going on and how I can keep my fish safe?

[chunkoblue]

My guess is that your tap water has dissolved gases in it that lower the pH down to 7.2. Try letting some tap water sit in a bucket with an air stone for a day to help let the gases escape, and then check the pH.
My tap comes out 7.0 but ends up at 8.4 after letting the dissolved gases escape.

[fishie111]

You were correct. I left some treated water out overnight (without an airstone as I didn't have one). When I first treated the water, its pH was 7.2; this morning, the pH was about 8.0.

So, now that I know what is going on, how do I handle this for water changes? I can probably "age" some of the water for my small betta containers (1 - 5 gallon), though I will need to mix in some tap water to get the temperature right, however I can't age enough water for my larger tanks that I fill with a Python.

[Star_Rider]

if this is due to off gassing I suspect your gH/kH is stable and this is what you really need to be concerned with.

pH in general doesn't affect the fish that much..if it did think about the impact CO2 would have on fish in planted tanks..my pH will shift down then back up after I turn the co2 off..no effect on the fish..

[chunkoblue]

This is why I have a 20 gallon and 10 gallon tank with heaters that I use to age water in preparation for cleaning my 55 gallon and other tanks... these dissolved gases are a curse! This is not uncommon for those of us with well water. Because of this I don't use a python, but I make sure I have 3 empty 5 gallon buckets ready for when I clean the 55, and I have more than enough water ready at the right temp for my water change.
Perhaps you could get a cheap 10 or 20 gallon to age the water in (check craigslist.com for sweet deals) and a heater. My tap also has ammonia (1.0-2.0 ppm) so I've got a HOB filter on the 20 gallon that oxidizes it down to Nitrate before doing water changes. If you have well water (or if not too), I'd check to see if your tap has ammonia as well. Good Luck!