Hi Ed,
I am not sure how much 1kg will treat as I have not measured that yet. I would say over 500 gallons depending on the TDS you want to hold.
As far as selling it, I am not doing that just yet as I want to try another month worth of testing. But I stated, for $31.00 shipped from the website I posted, you can make about 5kg of this mix. I have made 2kg so far and still have more than half of the mix left to make.
It is a good beneficial deal if you have a gram scale (needs to read 0.00) and some patients. Takes me about 15 minutes to make a batch.