Using driftwood and/ or indian almond leafs in your aquascape or peat moss in your filtration will release tannins which will lower GH
. It will also stain your water brown and give you a blackwater look to your aquarium. Your fish will like it, you might not. Carbon will absorb the tannins and clear the discolouration, but will also negate the GH
Chemically altering things generally leads to more issues than it solves.
The other option is to mix your tap water with either RO
water or distilled water at water changes.
Personally your level of GH
isnt that high. Its high end of ideal. I also wouldnt put much trust in test strips giving you an accurate test reading.
If you arent seeing any aggression between your fish I would put your issues down to the poor water quality they were in recently. See if things improve or deteriorate over the next few weeks now your water quality is better.