What I have. Established 40 gallon breeder all low tech with fluval 306, aeration thru sponge filters, neutral substrate, driftwood, 36 inch finnex stingray. KH 6, GH 6, pH 8. Temp 78.8. I have anubias nana, anacharis, wisteria, ludwigia, several crypts, java fern, amazon sword. I have a school of Columbian tetras, a school of red eye tetras, a school of Cory cats, one German blue ram, one Bolivian ram and several snails. I know every body says to not mess with pH but I have been slowly adjusting my waters hardness with distilled water which I finally got down to 6 after about 3 weeks. normally my tap is around Kh/gH of about 11. PH 8.2. My question is what do I have to do to stabilize my ph at a lower level. I don't know if I will do it since I have been doing pretty well with where it is at but more than anything i really just want the knowledge. I understand water parameters, but am new to planted tanks . This tank has been up for about 6 months. I know I can add peat and what not to buffer it down but when I remove it will it just come back up? Maybe I should stop aerating? All questions I would love answered. Any help would be appreciated!
I won't tell you whether or not you should do it, but if you really want to do it the best way would be to use a buffer. Peat, driftwood, etc. will lower it but only as long as they leech tannins. So yes if you remove them it will eventually just go back up after a few water changes. BTW I would like to point out that if you are lowering your pH you are lowering your kH as well so just keep that in mind. And don't stop aerating thats just going to cause more problems for the fish than it will help adjust pH.
The best way imo to keep it at 6 is to use a buffering substrate like controsoil or any of these active substrates. They will keep the kH near 0 and the pH locked around 6-6.5. These kind of necessitate using remineralized RO water though. The reason is because if you just use tap water you will use up the buffering capacity of the substrate quicker. This is a lot of work compared to just doing normal water changes.
The second way is to simply use pH down and adjust the water to where you want it as you perform your water change. pH down is sulfuric acid and like any other acid will eat through your kH to reduce your pH. Its easy to make mistakes and put all of your fish into osmotic shock if you make a mistake. Additionally if you have a low kH your pH is subject to large fluctuations easily, esp if you don't have a buffering substrate. Also your pH will only stay where you set it assuming that nothing in your tank is raising the pH, like crushed coral or certain types of rocks etc.
Lastly you can use a combination of seachems acid buffer and alkaline buffer per their directions to create a buffer in your water that should help stabilize the pH where you want it. Ideally you would adjust the water you are about to put in the tank at your water change before you add it to once again not cause a huge fluctuation of hard water coming in from your tap, then suddenly reducing it from 8 to 6 (which would almost definitely kill them).