I have used Cation resin 陽性樹脂 before, which replace Ca+, Mg+ by Na+ to soft water(reduce GH), but CO3-/SO4- (KH) remained unchanged.
I used a little power head to drive water into a DIY bottle. GH dropped to zero overnight but KH remained unchanged. Hardness rised gradually and resin change color(deeper), then I "recharge" the resin by salt water as instruction.
It work again after recharge but have less performance each time. Even worse, KH become out of control (max. 16dH after a month). Finally I removed it from my tank and plan to replace the substrate(with seashell).
FYI: anion resin 陰性樹脂 can replace CO3-/SO4- by Cl-(reduce KH), but it is recharged by hydrochloric acid, which is corrosive and hameful if not handling well. So I don't use them.
So I don't think you need to use them with good substance unless you are using well/spring water.
Sorry for saying too much, and hope help you some.