Your water could have a low pH caused by high carbon dioxide which aeration would correct. I would look at the gravel just to be sure it is not causing the pH to go up. Most of the time the pH would go down after being added to the aquarium not up.

The silk plants will not have any impact on pH as you pointed out, but something in the tank is raising the pH. The small volume of water in so small of an aquarium can be affected by anything that can dissolve in water, such as a rock or gravel.

I've put a small amount of gravel in a cup with some tap water to age 24 hours and see what happens. If it's the gravel, that would be an easy fix. Do you have a gravel brand suggestion for me to try. I'll go out tomorrow and pick some up for a test with my water and then proceed from there after I find the gravel that will allow my pH to stay stable.

Now, assuming the gravel is the problem and I switch to another that doesn't mess with the pH, how would I go about getting my tank switched over? Will changing out the gravel cause the tank to mini-cycle or will the bacteria in the filter be enough? Also, I'd need to slowly acclimate my betta to the new pH after I've determined it's stable. Geez, just when I thought I was smoothly sailing along. :)

I'm guessing I would put the betta in another container using it's existing tank water. Over the course of the next week I would slowly change out some of his water with the newer tank water that will have the lower pH. Then when I'm sure the tank is stable again and he's acclimated by the slow add process I add him back into the tank?

I'll be checking the gravel tonight and picking up some new tomorrow when I know for certain that's what it is.

Thanks for your input!
Judy

Judy, I think papa is on to something.
Let me give you a little longer version and see if it makes more sense.
Your well water probably has a buildup of CO2.
That can be from the well and also from the plumbing.
CO2, a gas, is acid, and will make your water more acid.
More acid = lower pH = 6.6 pH

After you put the water in the tank, you aerate it, or it just allows the excess CO2 to get out of it.

Then less CO2 = less acid and your pH will rise = 7.6 pH.

You were right the first time.

Try taking a bucket of well water, aerate it for a day or two, then check the pH.

Before you go to all the trouble of changing gravel, check your water first.

I have the opposite where I live.
Our water comes out of the faucet at about 9.4pH
After I aerate it for 3-4 days, it's a rock solid 8.2pH.

If your water is still low/acid pH after you aerate it for a few days, you can use just the smallest pinch of Arm and Hammer baking soda to raise the pH up to 7.6.
Add just a tad, and test.
Repeat until you get it where you want it.

Corrie, thanks for the input. I've got a cup of gravel & tap water aging and tomorrow I'll pick up a pump so I can aerate just a container of tap water as well. That way I'll figure out for sure what is causing my pH change.

Again, thanks for the help. :)
Judy

Judy, allow for one more possibility when you are testing the gravel.
The gravel could be totally inert and having no effect.
Sitting a cup of gravel out in water could do the same thing as just letting the water sit out with no gravel in it.
It could still be just CO2 gassing off.
Corrie

..... I think I have my answer of my pH change. I put a little tap water (6.6 pH) into a cup with some gravel. In another cup I put some tap water only. In the gravel that sat in it's water still and aging.... no pH change. However, after just a few minutes of bubbling it (I just used a turkey baster to blow in some air) the pH changed to 7.4. So, now for the water only cup I puffed it with air for a few minutes and the same change happened.... pH went to about 7.4. So, the answer to my puzzlement is the CO2 gassing out of my well water.

Unless I'm totally missing something I'm assuming what I need to do now is gass-out my tap water before adding to the aquarium for water changes? If so, I'll get a small pump & tubing to aerate my change water bucket.

I think you broke the code. ;-)

Okie dokie...... now that I have figured this out I'm ready for the next pH puzzle if you are willing to help me some more. My betta would probably like a slightly less pH than the 7.6 that I currently have. What is the better way to adjust this and keep it stable?

Judy, don't go chasing numbers. That always ends up being a major pain, problem, and sorta dangerous.
Fish need stability more.
If your fish came from a farm in Florida, it's probably used to a little higher pH than that anyway.

Well water is usually buffered pretty good. I'll bet your water will hold that 7.6 for a while, without having to add any buffers to keep it there.
As long as you do weekly water changes, and aerate the water first, it should be a breeze for you.
Check pH, check temp - match them up, clean and go.

Thanks! :)