The first option is to aerate your tank. Many aquarists would claim that this is also the best way to lower the pH levels in the water, but I'll leave this decision to you.
Using driftwood is a common method for keeping your pH levels lower. This is because driftwood releases acidic compounds known as tannins or tannic acids when in contact with water.
All you need to do is to add a teaspoon of baking soda per 5 gallons of water. This amount will slightly increase your pH levels and it won't harm your fish, shrimp, snails, or plants.
Take some crushed corals, put them in a bag, and add them to your filter. This will gradually increase the pH values without shocking your fish or making your tank too dirty.