...Although, I added driftwood, peat, and CO2 in my tank (all natural ways to lower pH) and now my tanks sits at a stable 6.8 pH....
Right on. in order to achieve an acidic pH in your tank you need to accomplish 2 things.
First, you need to use up all available alkaline buffer (KH) in your tank.
Second, you need to have a constant source of acids in the water.
First you need to measure your KH and know where you are starting from. If you have a pH of 8.7, it is likely your KH is extremely high.
With a lower KH, you will need a lower level of organic acids sourced into your tank. Depending on the volume of your tank will be more cost effective.
First, you can start with pure RO water, re-constitute with a natural alkaline buffer like, baking soda (sodium bicarbonate), crushed coral (calcium carbonate), or seachem's alkaline buffer (blend of bicarbonate salts) all are natural ways to increase your KH from 0 to a target level (2-4). Using baking soda or the seachem product will allow for a more precise measurement.
If starting with 100% RO, you will also need to increase your GH to a level at least equal to your KH. Crushed coral will add to your GH (calcium), you can also add other mineral blends such as Kent RO right, Seachem Equilibrium, Seachem Cichlid Lake Salts. All are natural mineral additives that will increase your GH to a desired level.
If you know the GH & KH of your tap, it is also possible to do a certain percentage of RO water to tap water to achieve desired parameters. In my opinion this is not as easy as re-constituting pure water with minerals.
If your tank is already filled, you can use seachem alkaline buffer to convert KH to CO2. This will lower the KH for you and once your KH is achieved you don't need to use it any more. Seachem Acid buffer is made of bisulfate salts, which is a weak acid compound. I've used it and it worked well for me.
The second step is to have a constant source of acid to keep your pH down. driftwood, peat, & CO2 work.
