Originally Posted by Brandonl87
Hey bryon ok they said kh is 80 an gh is 20.
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OK, those numbers must be in ppm, so GH of 20 is roughly 1 dGH or very soft. The KH at 80ppm is about 4.5 dKH. That's not high, but it will buffer the pH of the tap water to some extent.
In this situation my suggestion would be to use mostly "pure" water for the tank, this can be RO, distilled or even better rainwater. The latter will be acidic, which will help more. Once the tank pH is where you want it, water changes with tap water should be OK, but you will have to experiment a bit with volume. The aquarium biology factors into this, so it is specific to the tank.
If there are fish in the tank, go slow. As you are already doing water changes with RO, I would use rainwater, maybe 1/5 of the tank volume. And bit by bit.
One can buy chemicals and stuff to achieve this, but I prefer doing it naturally. It is less expensive, safer and more long-term.
I have a similar related problem, my GH and KH is less than 1 so the tank pH will easily drop to 5 or perhaps lower. I'm having to add GH for the plants, but the pH I leave alone because I have wild-caught soft acidic water fish.