The water in my NPT has gotten softer and more acidic over time. KH dropped to 0 and pH was so low it was unreadable. Though, that may have been due to overstocking....DataGuru said:That's a Diana question.
Seems like soils tend to get acidic at first and then return to neutral over time as the soil gets used to being submerged.
I don't think it's absolutely necessary. and you're right. Bettas like softer lower pH water.
I would think that water in NPTs would get harder over time from evaporation and topping off. They shouldn't have the issues normal tanks have with KH getting used up by the biofilter bacteria and pH slipping down over time. From what I've read tho, in heavily planted tanks, you see larger pH swings daily with lower KH. and in some cases if the water is low in calcium, pH may move above 8.4.