What hasn't been asked in this thread is, what is the chemistry of the water coming out of the tap, used to change the tank water?
Most municipalities will have a in depth chemistry make up of their tap water for the asking if they're anywhere near honest. I know our previous city did so, you could get a monthly report on dissolved gasses, solids, minerals, trace elements, and possible bad chemicals.
Since we're on a well system our water is a lot more stable because of no chlorine, and seasonal CO2 because of heavy rainfall adding, but the chemistry is less friendly to plants so I have to add trace and iron supplement.
Folks whose tanks are doing great with little input other than frequent water changes are probably benefiting from the chemistry of the water straight from the tap.
Starting small, keeping it simple.