Reverse osmosis, even reverse osmosis with deionization, cannot and does not produce pure water. Only distillation can make that claim. It is very, very clean, but not pure.
i have a float switch and a 50 gal res that stays full of RO water and will sit for days or sometimes even a week before i touch it and i see none of this as a benefit in my experience. weather it comes fresh from the ro or sat for a week my ph seems to be about the same. if you're ph is adjusting sitting out over night (uncovered?) maybe airborne sediments are landing in it or residue in your storage container are contaminating your ro water (contamination first but the word is really overkill) and adjusts your ph. idk just never worked that way for me and i've been through at least 1,000 gallons of RO water in the last 5 months.
regardless nothing will make it easier to adjust the ph where it does not swing one way or the other drastically but a buffer! if it's pure water and it sits for a year and is still pure water you wll still have that issue. this is why your flushing water needs less ph up/down solution to move 1 point then your water with say 800ppm nutrients needs. which may be double the amount or more.
Hey X, don't we both have RO/DI units from Pure Water Club? My RO/DI water always comes up in pH as it sits out, like G,ro says. Never higher than a 6.8 so far, but that's fine for my uses.
hey Sirus,what's up?
my water goes to 7.0 after a day but initialy comes out much lower.no CO2 in the work area and holding drums are sealed.
have you tested your ro right when it is first filtered?
This is my experience and observation, and if my record-keeping skills are good enough for the likes of large public aquariums, then I think it's safe to say that they're good enough for Mary. I have considered a few answers as to why, but without other testing equipment it's all guessing.
First, I know that the minerals that make the source water both base and alkaline have been removed. I already know the parameters, in terms of pH, German (dKH, 9 degrees out of the tap) and general (GH, usually over 10 degrees out of the tap) hardness of my source water using a titration colorimetric test kit (which, with a little calculating along with pH can give a number for the CO2 dissolved in the sample). I can assure everyone that it changes significantly when passed through the RO/DI--stabilized at that 6.8 versus 7.4 to as high as 8.4 pH.
Second, that water, which in my case comes from a pretty deep well, has spent some time under pressure before coming very gently out the other end and I already know that agitation equals CO2/O2 exchange, as well as the fact that atmospheric CO2 can and will change the pH of water in this condition.
So, why do I see such a huge fluctuation in pH readings between newly filtered water and water that's been in my trash can for a day or six? <shrug> I don't know. I know it hits an equilibrium, but I cannot state unequivocally that it's CO2/O2 saturation, or that it's anything else. I just know what I observe.