One thing I did for a while was a nylon mesh bag of cation exchange resin placed near the filter intake. I had a problem with something in the tank raising my GH, so I used the resin to mitigate the GH rise while I sought out the cause. Cation exchange resins are a part of RO systems - they remove things like Ca/Mg (also some of the traces) and replace them with either H+, Na+, or K+. Obviously the H+ is a bad idea in the tank - pH crashes. So, find the sodium or potassium based resin. You could also use it to pre-treat your water-change water before adding it (put in a 5-gal bucket of tap water and aerate for a few hours). The resin can be regenerated with a concentrated salt solution, rinsed, then reused.
72g bowfront planted, CO2, 4x - T5HO, Eheim 2213 and 2217, 2 angels, pristella tetras, blue tetras, betta, albino bristlenose pleco, albino cories. Sword, vals, hygros, ludwigias, java moss and fern, anubias
2g Mac-quarium. Clown gravel, fluorescent plastic plants, and 2 guppies.