Why does PH Rise after Brewing a Fresh Batch of Nutrients?

Start with water and add nutrients. Our nutrients are usually pretty acidic, so the PH drops. We then adjust back up to where we want it.

Over the next day or two, the PH rises, then stabilizes back down again after awhile. Why?

Maybe this is a stupid question, but what is the actual cause of this PH spike?

Ive noticed the same thing, and always thought that its because the source water has a pretty high PH. I try to skip (unless its really crazy) altering the PH right after adding ferts. Because as you said, pretty much the next day it comes right back. I cant do it that way all of the time, but when I can I will.

I ask because I'm currently running way too many plants for the size of my DWC reservoir. Most of the time this means PH dropping like mad, around .2 per hour. Sometimes though, it mysteriously locks into place and behaves. When it does, it's like I'm able to catch that PH upswing and, if I hit it at just the right time, peg it for awhile. I'm trying to figure out what's actually going on so I can either take wiser action or maybe use it to cheat by with this small res.

Yes, I often wonder myself about whether the strain(s) have anything to do with it. Once, I had DP BB and it kept bringing down my ph like you said about .2 an hour. It was crazy. Everything as far as I could tell was spot on, white roots, my res looked pretty good, and the plants looked amazing. But, still the ph kept dropping no matter what I did. This was week 2 flower and week 4 flower. I was certain that something was wrong..I kept re-checking my probes for calibartion, but they were exact and didnt require calibration.. What I found out through the grapevine and alot of worrying is that, the DP BB are prone in those weeks to potassium deficiency. Adding the PH up, solved that...Anyway, everything turned out good, I mean really good. And I learned to chill out a bit and just roll with it. For me it was a good lesson, but it also made me wonder what other strains are like that....

You know that's a very interesting idea. My ph drop just arrested itself somehow, and it's right around week 5 flower. Maybe there's something to that. I never would have thought to investigate potassium deficiency.

Do you mix your nutrients and then allow them to stabilize for at least twelve hours? I use the Canna Aqua line and to avoid the ph fluctuation I just mix the A and B parts into two separate jugs the night before and that seems to give the ph time to stabilize. just my two cents

Nah I dump em right into the res. 24 hours later is usually when the PH starts creeping up though.

Shameless bump. Nobody has good chemistry knowledge to drop on us here? Surely there is a faily basic explanation for this, no pun intended.

ph rise is normal for dwc, your adding alot of air to your water, air being neutral. you want your ph to swing a little so all nutrients become available. set it 5.8, let it rise, set it back the next day.

what happened to all the smart helpful people on here, this used to be the best forum...

agreed but i want to know why it happens. i can't see air causing a full point in ph rise or else we'd all be in serious trouble with bubble stones.

You have to get better ph down. I myself use sulfuric acid and my ph stays between 5.8-6.0 for 2 days but I check my ph 2 times a day.

you dont want your ph to stay at 5.8

a wide range of nutrients are available at that ph, but not all of them. you need to let it fluctuate or else you'll get lockout.

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but eh, wtf do i know. ive only grown thousands of plants in every system imaginable

Ec goes up, PH goes down=plants require less nutes.
Ec goes down, PH goes up=Plants require more nutes
Ec stable, PH goes up=Equilibrium=Good thing.

water in dwc will evaporate as well as plants drinking water so it is always best to have either a large res to buffer the ph shifts better or have an auto top up res.

I know all this, and agree with all. The PH is not a problem for me, it's under control, everything is fine.

I simply want to know why this happens. What is the chemical reason that ph goes down after adding nutrients, but swings drastically upward for the next 48 hours?

Again, this is not a problem in my garden, I just want to know why PH will go up for awhile after adding acid to the mix.

it could be your temps changing. after your water is in the res for a while, its getting closer to the room temp. temps and ph have a reverse correlation. basically this means as your temps go up, your ph will go down. as your temps go down, your ph will rise. wait until your water temps are stable before taking a ph reading. for best results they say keep temps at about 68F and ph 5.8-6.2

I actualy looked into the temp vs ph connection when inititally looking in to this. You're right, there is a connection, but it's nothing close to causing full point PH swings. It's a very, very small PH change based on temp. I'll see if I can dig up the paper that I found on it.