You can get the jbl peat pellets that go in your filter that have both a fast acting and long term effect on ph but you can also buy peat balls on ebay but they just sit in the tank. It will tint you water though and can't really use carbon to clear the colour as it counterracts the peat benefitsAnd i answered my own question by looking at the first post of this thread lol!
So what is that thing u filter through to loser pH? 😛
Most of the specialist plant substrates actively lower ph to a degree but dpends how low you want it