So I purchased a pretty decent electronic PH tester-
My filtered tap water has a Ph of about 8. I’ve been adding Ph-down with citric acid to get the Ph to about 6.5 and then watering my trees. Only thing is the next day I check the left over water in the can (galvanized metal) and it’s risen to close to 9.
Just curious if anyone can explain what is going on? I stir the water before testing and make sure my Ph tester is accurate so this reading should be correct. But why?
Interesting you posted about this. I experience the same thing. I will be following for an answer for our sciency folks 
Let your water stand for 24 hours. The pH will change due to temperature and gas exchange. Then adjust the pH value and than try the ph again a day later. Let us know if it is better. 
@Bernd62 I’ve actually tried this as well- taking the water out of a water tub that’s been sitting for several days. And although it fluctuates less than the tap water, it still has a high fluctuation.
Im now reading on some hydroponic forums that citric acid is not very stable and this is very common.
@SoCalNative - what is the active ingredient in your Ph- down? Mine is citric acid. Wondering if there’s a more stable acid product I could be using
I use a phosphoric acid containing pH down which seems to be reasonably stable. I mix up a fairly strong master solution that is then diluted into a 5-gallon bucket for injection into the hose line. Getting an upgraded injector for this coming spring.
Try your citric acid containing pH down in a plastic container and see how much the pH changes. You may be forming a bit of Zinc citrate in the galvanized watering can.
I am using distilled vinegar and it’s easy enough to add more. I have also been adjusting the pH each time I use the water out of it. I keep it in an open bucket to vent the chlorine and just add water to keep it topped off. I am also using RO water. I keep mine in a 5gal Home Depot bucket.
@MartyWeiser Do you think a closed container would have the same impact?
A closed container might keep some of the acetate from the vinegar from evaporating (why you can smell vinegar), but it is probably a small effect. My master solution is in a closed container (gallon jug) and the solution for injection is well vented (1.5" hole in the top of a loose fitting lid on a 5-gallon pail).
I am using 5% regular household white vinegar and I see it will hold for a day or two.
It actually holds longer then my PH down product.
I pull the tap water from the faucet, let it sit in a bucket for 24-48 hours and apply the vinegar right before use.
The left over water seems to hold PH for a day or two.
You could experiment with vinegar and see if it works better for your situation.
How much quantity (more or less) of vinegar are you adding?
I tried it with vinegar, about a tablespoon per gallon, and citric acid Ph down- maybe 1/2 teaspoon per gallon, both get my Ph in the 6.2-6.3 range.
I’m thinking neither is a very stable solution, but also what Marty said about leaving the water in the metal can makes sense.
I just did a test with glass jars and the Ph rises within hours, but not nearly as much as when the water is left in the can.
I’m going to try the test with some phosphoric acid Ph-down product when it arrives next week.
But leaving the water in the can seems like a big no-no.
I’ve got a small balcony with no water hookup and a lot of trees so filling up the watering can and carrying through the house is a whole ordeal which is why I tend to leave water in the can.
Also sorry I tried the search function and didn’t come up with much but once I made the post It lead me to “related topics” which now I’m reading through and it seems this is a common thing. Vinegar or citric acid Ph rising within 24 hours.
Makoto, Do you water with a can’ I been adding PH down to 2 gallon water cans and watering by hand every day, the temperature does affect PH levels, so use all the water at each watering, make new each watering. I started in 2023 every watering - I dont miss any – except rain storms where the trees seem to stay wet longer than when PH lowered can water is used
Hi Steve,
By this hand-water-ph down procedure, over this long period of time, have you been able to observe any significant shift in soil pH? Have you ever measured it (soil) before, during and after this repetitive water pH correction?
This is a general question to anyone who has relative experience and this is why I follow this topic.
The soil is so porus that I skip it and I check the water PH . I know that checking the drainage water is a way to go as well. The trees look healthier, the acidity helps their roots function , so at initial watering with nutrients is the place that Im expecting the lower PH to help with tree function.
I ran some tests this summer as my tap water is over 9. I bought pH down (phosphoric acid) made by Humboldts Secret and it seemed to hold for a few days. I had the water in a 4 gallon plastic backpack sprayer. I’d like to incorporate the right product into a system for my drip irrigation. I’ve read that vinegar and citric acid typically don’t hold for longer than a day or so.
tap water has chemicals added to create alkaline water to avoid leaching metals out of the pipes. very much being done post the debacle created in Flint, MI when they used surface water that was acidic and leached lead out of the pipes. the chemicals tend to strive to create alkalinity and “save you” so to speak and have buffering capacity I suspect. Citric acid is a very weak acid. it is probably undergoing secondary reactions later on and losing its ability to adjust the pH downward. maybe use a stronger acid like acetic or phosphoric and see what happens. do not use hydrochloric. chloride is bad for plants. Possibly explore getting a system that changes your water chemistry by pulling out some of the city provided “extras”. explore blending your city water with RO water? I think too many people think water quality is the most important factor in raising bonsai. doesn’t seem that way to me. you can also add an acid fertilizer to the top of the soils and that will neutralize some of the alkalinity you are experiencing. there is too much fixation on the perfect pH in my view. relax a bit and look at the trees. how are your trees behaving?