I have to disagree on the above. pH is negative LOG of hydrogen ion concentration, which means that it only swings upon large amount of dilution, say 10 to 100 times. To achieve this, you need to do almost 100% water change, and we don't usually do that especially when you haven't done WC for a while. Besides, by the time you do 100% WC, you also remove all the ammonia in the old water, so you no longer need to worry about the pH swing. It is a valid point, if you have very sensitive fish to pH change, but in terms of ammonium/ammonia equilibrium, it won't happen.
On another note, I used to keep a 6 gal tank with some neon tetras and ghost shrimps and also some low light plants and it worked out great until I upgraded to my current 10 g. It doesn't look like a huge difference between 6g and 10g, and yet, it is so much pain to keep up with my current tank (although now I planted my tank heavily and going high-tech, so that is probably why). I also thought that my stocking was limited due to the water volume, but if you google 'nano fish list' you will find a plenty of stocking options you can afford with your tank size. Most of those fish are a bit rare, so you will only be able to find them from online vendors or good LFS nearby, but it is worth searching if you want some nice looking and tiny fish. I know a smaller tank has a smaller margin of error, but it is so much easier to keep up with water change and tank maintenance. Just don't do a complete tear down next time. Good luck.