I'm using the Primo for my second grow. In my area, the 5gal jug is $12 bucks but then it's exchange empty for full for like $6 or $7....
I live in the mountains and our house is on a well so no treatment of any kind until it gets to the Culligan in the garage so the hose water
is untreated...lots (LOTS) of minerals and sulphur. So I cut my Primo 80/20 - 70/30 with well water. The Primo doesn't have a TON of minerals
added back after RO so I think the untreated, mountain well water bumps the ppm up and allows the GH UP & Down to grab better (more stably).