Hi, welcome to the forum
Lowering the pH with chemicals is not a good idea.
Fish that like a low pH usually like soft water. Soft water is defined as water that has few divalent metal ions (mainly calcium with some magnesium and trace amounts of other metals) but it also has few minerals of every other type. Adding a chemical does not remove any minerals, it adds to them - the opposite of what these fish need
The other danger is that high pH usually goes with hard water, and high GH usually goes with high KH. If the KH is high, as soon as the chemical is added the pH drops, then the buffering effect of the KH kicks in and the pH goes back up again. This constantly swinging pH is not good for fish. The fact that your driftwood is not affecting the pH does suggest your tap water has high KH.
Hardness is more important to fish than pH. If your tap water is hard, you need to reduce the hardness for soft water fish. This is done by adding a source of pure water to dilute the minerals in hard tap water. The usual 'pure' water is RO (reverse osmosis) water either purchased form a fish shop, or from a machine installed under your sink. The same ratio of tap:RO must be used at every water change; an emergency water change using just tap water can never be done so there must be some RO on hand at all times.
Now that I've said all that, what is the hardness of your tap water? If you don't have a tester you should be able to find that info somewhere on your water company's website. You need both the number and the unit as they could use any one of half a dozen units and you'll probably need to convert it to one of the two units used in fishkeeping.
Dwarf gouramis are OK in water up to pH 7.5 and hardness up to 15 German degrees.
One more thing - a lot of people find dwarf gouramis die within a few months of purchase. Dwarf gouramis bred in the far east are often already infected with dwarf gourami iridovirus by the time they get to the shop. This disease is incurable and is the cause of so many of those deaths. This applies to all the colour morphs of dwarf gourami. It is for this reason that a lot of fishkeepers won't buy dwarf gouramis.
So, a few things for you to think about.
Are you willing to risk buying diseased fish?
Do you have hard water?
If you do have hard water, are you prepared to accept the cost and messing about with your water just so that you can keep softer water fish?
