What I plan to use (every time I go out to do it, something comes up and I don't get around to it) is Sodium Metabisulfite, bought off Amazon. I researched the "advertised" preservatives, and this is all it is. I need to look up the concentration again, but I plan to use 4" pvc as holding chambers. It was on my to do list today; but planting apple trees took a lot longer then planned. Hopefully next weekend. I have cycled water through them post season to keep them wet.