example: So I pH my water on Monday will it be the same come Friday? curious of opinions I am sure there are many factors that would or would not allow it to stay stable.
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@Smokin_ernie I don’t have an opinion on this but can offer my observations.
I store my water for several days to up to a week. Fresh from the tap my water pH is about 7.5, after several days it is above 8.0. I have also seen that the pH drift is greater over time but does stabilize at around 8.0.
I have several theories as to what the mechanism is, but the long and short of it is that there is clearly an interaction with the air and/or the out gassing of dissolved gases that likely affect pH.
What happens with water that has been adjusted for pH? I have not done that experiment yet but suspect that similar pH drift will be observed. I also suspect that the amount of, and the specific dissolved solids in the water (i.e. water hardness) will have a huge effect on whether or not the pH drifts and how much it drifts.
This didn’t really answer your question but it does give you some preliminary information.
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Thanks @merlin44 good info! I kind of figure there is no direct answer anyways with all other factors. Time to do some experiment to see how long it stays stable.
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I got in trouble during my first coco grow by thinking I could ph a small amount of water for the first couple of weeks and work from that. Big mistake.
My experience is that your water will drift over 24 hours and requires adjusting. Over time, the amount of drift slows. If you were to ph 5 gallons of water daily for a week it would eventually stabilize. More solids in the water resist ph change more than pure water and retains ph better as well.
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I have also experienced the drift problem
And have also noticed since using ro water it doesn’t drift as much
Good point and observation @Myfriendis410
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I don’t know if this will help but this is a little trick that I do. I grow in soil so I always shoot for a pH of 6.5. But if I know I’m not going to have a lot of time, say the next night to water some of my plants, what I do is I will pH my first gallon of water at 6.3. Then I know it’s safe to use for that night . then the next day or the day after I will come in and use that same water Cuz I know from my environment and water that it will not rise above 6.8 for a few days.
This is not a common practice I do though. I try to to pH my water or nutrients right before I’m going to use them.
Take care have a nice morning.
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This is all great stuff thank you!! It does help and hearing real experience is priceless info!
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I try to vary my input ph somewhat: nominal ph for most waterings and an occasional watering at the bottom of the proper range for the medium I’m using. This takes advantage of the natural tendency to rise in ph and opens up different nutrients to the plant.
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I started pHing 50 gallon barrels and I check the pH weekly because I noticed that it will go back up from 6.5 to 8.0
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I’m glad you asked this question. I was going to reuse my 55 gal water barrels from last years veggie garden , but hesitant since I now know about ph 
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Best to just check and adjust right before watering. I did take the time to ph 1 gallon of water for some coco seedlings and it took a week to stabilize my tap water. BUT! That’s 500+ ppm so that would buffer it somewhat.
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@Smokin_ernie @merlin44 is correct on this. TDS/PPM With calcium carbonate and other natural minerals have the ability to buffer PH longer and remain more stable than water that has almost no TDS/PPM such as reverse osmosis water. Well water (if you have it) may have a lot of stuff in it, but remains the most stable.
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I do have well water. So it seems that checking every time I water is a good practice to get into.
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