You don't need any of that shit in the water if you have a matured tank. Get yourself a small heater, set to what your tank temp is, makes water changes a lot easier and you dont have to wait 12 hours for the water to be up to temperature. Another thing, get yourself a decent cannister filter i.e Eheim 2215/7 depending on how much water it holds. You wont get any problems with water quality, and you also have enough filter media for bacteria to colonise. Only need cleaning out every 6 months by giving them a flush with tank water.
Test the pH of your water before messing with the tank though, or u'll end up going to low or to high. Tetras can live between 6-7.5 on the pH scale.