HELP! Very strange problems with pH

[azorahai]

I'm growing a few plants on a mix of peat moss, perlite and vermiculite, and I'm having some very strange problems with the run-off pH. In order to raise the pH of the mix — it was getting dangerously acidic, reaching as low as 4.8 — I've been flushing the plants until the run-off registers a very low ppm and the pH is somewhere around 6-7, and just as all the excess water runs off I immediately feed them a solution with a pH between 6.4-6.6, in the hopes that it'll maintain this level until the next watering/feeding.

However, even though the last drips of water that runs off after the flush registers a pH of around 6-7, as soon as I start adding the fertilizer (again, with a pH between 6.4-6.6), the run-off starts trending lower and lower. I usually prepare enough solution to match the pot volume, and even after this second "flush" with pH'd nutrients, the last run-off ends up registering a pH of around 5.0, sometimes even lower.

I have no idea what is happening. The pH meter is fine and is regularly calibrated, and I also double check everything with pH strips just in case. I'm using a sodium hydroxide (NaOH) solution to increase the pH, and before that I was using a sodium bicarbonate (baking soda, NaHCO3) solution, but that wasn't working too well and I always ended up with a solution with way too much sodium in it. With the new solution, I'm registering a 50-80 ppm increase in total dissolved solids to bring my most acidic solutions up to the recommended levels. Can someone chime in on what may be happening?

[JeffInCanada]

[azorahai]

Our problems seem to be different, as their pH is slowly drifting downward over the course of several days because — it seems to me — nutrients are building up. In my case, in the exact same day, the pH goes up as all the solubles are washed out by thoroughly flushing the pots with tap water (~7.2 pH), and then goes immediately down towards 5 pH or even lower as I add a nutrient solution measuring 6.4 pH. My theory is that some sort of reaction is taking place, but I have no idea why.

[Rwise]

Peat moss has a PH of 3.5, what did you put in to balance that? I use a bit of peat in my 8.4 soil to get the PH down.

[azorahai]

I should have amended the mix with dolomite lime, but this is my first grow so I didn't really know this was necessary. In any case, I wasn't having this bad a pH problem until about one to two weeks ago, and I've actually decreased the amount of nutrients I'm giving the plants, in addition to regularly flushing the pots before feeding them.

[azorahai]

Let me rephrase my problem: I'm regularly flushing my plants until almost all solubles are washed away and the pH rises to 6.0-7.0, and immediately feed them a solution measuring 6.4-6.6 pH. As soon as the solution starts dripping from the pots, the run-off pH begins trending down. As I continue adding this solution — until the run-off registers approximately the same ppm — the pH keeps going down, from 6.5 to 6.0, and then to 5.5, and then to 5.0, which is whereabouts it remains.

[9fingerleafs]

Switch to coco. Chemistry is complicated and you'll probably have a hard time finding out whats reacting to what creating what, know what i mean?

[Rwise]

Check out liquid lime
https://www.google.com/search?q=liqu...ient=firefox-b

[JeffInCanada]

Do a test. Measure the PH of some water. Let it sit in a small sample of your peat moss (not from the pot the plant is in, from the peat moss bag) for a minute or do a small runoff test with a small sample of only the peat moss, see if it effects the PH of the water at all.

[dilvish]

I have never checked my PH run off and all my grows are soil. haven't had any issues. All I do is test the water going in as the nutrients are absorbed through the water uptake not from the soil. Some soils hold on to nutrients that's why some growers prefer coir or hydro.
Your soil medium uses peat and vermiculite and perlite. The "dust" or finer particles that drain with the water are likely what is brining down the PH, especially if you have more perlite and vermiculite than you do peat.

[Rwise]

How do you raise the pH of peat moss?
If alkalinity levels are so high that they cannot be controlled with sulfuric acid safely, then reverse osmosis, pond water or city water may be the best alternatives. Second, peat moss in the growing mix is very acidic, so it's necessary to add limestone to help bring media pH up into the desired range.

Does perlite change soil pH?
Both perlite and vermiculite are pH neutral, not altering the pH of the soil mix. They differ in their ability to buffer pH changes. ... Although both can hold plant nutrients such as those in soluble fertilizers, perlite has a low rating and vermiculite is rated as high.

I find perlite combined with other things in the soil does effect PH.

4.4
As noted above, peat Moss has an acidic pH, generally in the range of 4.4 (a pH of 7 is neutral; higher pH numbers indicate alkaline soils).