Wow. Thats an insanely low price for all that.
I would want to know what the tech is in the DI filters though.
If you are curious about your water hardness, you can get a very very rough idea easily. Just put a small amount in a container with a dark bottom and let it evaporate. if you see water stains, your water still hard to some degree. You wont know how much, but its a rough idea.
I personally like haveing moderately hard water. That hardness will automatically cause your water pH to increase after you pH down. How fast it goes up will depend on how hard it is, how concentrated your nutes are, and how much you aerate the solution.
I take advantage of the pH rise by pHing down to 5.5 or so, then letting the solution rise to 6.0 or 6.1 max, then pH it back down. This allows your plants to get the max benefit from different pH levels as far as absorbing different nutes.
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