Using the grocery store water is a good start, but ultimately it's going to be another chore and expense that would be better addressed by getting an RO DI system. I'm pretty sure that the water from the store is RO (reverse osmosis) only and it will still have some TDS (total dissolved solids) in it. The DI (de-ionization or demineralization by ionization) stage of a RO DI system will bring the TDS of your water to 0 so you're mixing your salt in absolutely pure water. Check out some of the threads and info on RODI systems and you will find plenty of information. The initial investment may seem costly and although I don't know what your store charges for the bottled water, in the long run you will have better results and save money with your own RO DI system, especially with a 72 gal tank. The trips to the store for water will get old fairly quickly. As mentioned I do fairly large water changes on my 77 gal, about 25 gallons each time and I would not enjoy hauling that amount of water from the store every few weeks.
|