My tap water rings out at a pH of 9.5 after a 2 stage filter. Ive always use a pH down but it seems like a bloody roller coaster! I tried using water collected in my dehumidifier which is essentially distilled water and it tested 0 tds and 7.5 pH and it worked great! Didn’t need to add pH down. The nutrients brought it to perfect range. So i bought an ro buddy thinking it would reset pH, but it did not. Thinking a deionization filter was the key, but no.
Point of all this is i would very much love to start with water that doesn’t need to be artificially adjusted but I’m running out of ideas. Rain water? Distillation would require a lot of costly energy to produce enough volume and takes up a bunch of space.
Any ideas would be most welcome! Getting a headache from beating my head against the wall
Do you aerate your water @Rockdog62
The reading isn’t a valid one, as pH meters drift when no ions are present in a solution.
Distilled, RO, and deionized water do not have a pH. A pH measurement is a reading of the charge balance of the ions present in a solution. RO water has no ions, and therefore has no pH. The only time your feed should be pHed when using RO is after nutrients are added. Adding nutrients adds ions, and therefore a creates an environment where a pH can exist in the solution.
RO will take on the pH of the media into which it is introduced.
Good point. Aeration of water will dissolve CO2 in the solution. That dissolved CO2 (ions) is partially converted to carbonic acid, creating an acidic pH in the solution.
What’s your Tap like before the 2-stage? 
I buy RO water from a water station for 1.50 for 5 gallon jugs. Denver is still in the process of replacing the old lead pipes with new and the city sent us a Brita 3 stage Carbon filtered pitcher to use for drinking water while they do the repairs. Even so, I still like to use the RO. Cheap and close.
Whatever the source, it needs about 250-300 ppms minimum to hold the pH and affect the rootzone instead of the rootzone pushing your water around.
SOLAR STILL
You can make a solar still, which would work well in places like California. It would give you pure water, no waste water and be free to make pure water, it just requires a bit of sunlight.
Get a large plastic storage container and put it outside in the sun.
Pour a bucket of water into the storage container.
Put a clean bucket in the middle of the storage container. Have a clean, non-porous rock in the bucket to stop it floating around.
Put the lid on the storage container.
Put a rock or small weight on the lid in the middle, so the lid sags above the bucket.
As the sun heats up the container, water will evaporate and condense on the underside of the lid. The water will run towards the centre and drip into the bucket. When the bucket is full of water, you put it into a holding container and put the bucket back in the storage container with another bucket of tap water.
You get pure water with a pH of 7.0, 0 GH, 0KH and no wasted water, no power used and it’s cheap to set up.
Well said @MidwestGuy and gromies happy growing my friend’s
Pretty much the same but higher TDS of course.
So how does one go about this? Airstone and pump?
Thanks! Great info indeed!
@Rockdog62 Get one for aquariums fish tank all yall need my friend happy growing
That would be explain a lot! I suppose I have a few erroneous assumptions that I need to sort through 
I start all grows with ro, but move to tap once they’re rootered. I used citric acid and potassium bicarbonate to adjust pH) I used to grow using hard well water (pH 8.6), zero chlorine. Now, I use city tap water, similar pH but with chlorine. I bought a rv drinking water filter to help remove the chlorine so I didn’t have to mess with additives.
That being said, bc I use organics in coir,
the safe pH range for input is anywhere from 4.5-6.0. Using RO in coir or peat, beyond starting, can lead to worse pH issues down the line, due to those missing ions helping to stabilize things.
Found this very interesting! Still trying to unpack a bunch of it.
RO appears unstable because it has no pH.
Again, a pH meter measures the change balance of the ions present in a solution. As no, or limited, ions are present in RO, no pH can exist.
I thought i read somewhere to not use dehumidifier water because it can contain pathogens or something, thats why i buy 5 gallons of spring water every other day, my tap water is so hard and i dont want to mess with the plumbing under sink to add a unit for water and risk causing a leak under sink
Hey Boogy Happy New Year, I will say our water is very hard, 385 ppm and 7.6 ph, its all I use, adjust my feeds accordingly and I dont get nothing for issue as of yet, had a touch of Cal def once for 2 days. Seems to be good water for my grows, it is from a well.
Why do you object to adjusting the pH of your water/nutrient solution?
I use my tap water which is very, very hard with a pH of 8.5+ (after aeration).
My tap is 450 ppm and 7.3 ph and chlorinated
Thats brutal, chlorine can be gassed off ,but damn 450 ppm is high!