i found that over time, waterchanges just cannot replace all the minerals and elements depleted by the inhabitants' needs. don't forget that magnesium is also required to metabolize calcium. i held off for years from buying the more complicated or expensive test kits thinking that my
lfs was just trying to sell me more stuff. when i finally bought more kits, i was surprised how off some of my requirements were. remember a waterchange can only replace the magnesium for only the amount of water you replaced.
