Ph problems late flower dwc..?

[Mazeblue1]

Dwc wedding cake week 10, plants look good, some foxtails but I read could be several reasons for that including genetics.I did a Rez change a day early last week because ph was dropping to 4.5 ish I would raise it back up by topping off with waterand by the end of the day was back down..? Now, 2 days later I just checked and ph went from 5.7-4.5 overnight again.. I’m not sure what to do, I do not want to do another reservoir change, I feel like I’m wasting nutrients.
Using gh nutrients for the first time, leaf temps around 77-79 during day, last night let temps get down in low 60’s since I’m in late flower but usually around 70 at night, 4 plants all very different looking.. any suggestions or advice?
Ppm’s at about 400, well water with about 150 pm’s plants are still eating but ph is brzerk!
maybe this is normal late into flower, I do not remember from my last grow if that happened but I was using advanced nutrients.

 

[Mazeblue1]

Hey thanks for all the help I figured it out myself like usual anyways..Nothing like checking this thread 100 times for no responses

 

[airedog]

Probably because there does not seem to be a definitive answer; lots of theories, and the cause may often be multi-factorial. There is some discussion in some UnderCurrent related threads. While there are many who can tell you how they got a good harvest despite the wild swings, there are few, if any, who can tell you how to consistently stop the swings from happening.

I've had similar problems in DIY RDWC as well as UnderCurrent and they usually start about mid-flower stage. I've heard recommendations of full recommended strength from both UnderCurrent and Advanced Nutrients, which isn't really possible as UC recommends much lower strength nutes. Even with pH Perfect AN formulations i've had those huge drops and i'm generally good to about 4.3 or so at which point i'll do a res change (i've had it go to 3.7). As you said, 2 or 3 res changes a week in a system starts getting pricy.

I also flushed for 2 weeks, starting with Flawless Finish and ending with just RO water; doing multiple changeouts until i'm under 50 ppm. I'm just coming back to growing after a 3 year hiatus, so i may not be as up to date as others here.

For myself, i am concerned when it happens but i try to rely on how my plants and bud look overall; your pictures look great so you're obviously doing something right. Wish i had a more helpful and definitive response.

 

[Edinburgh]

Same thing just happened to me, my ph was low in late flower last 14 days, flushed plant and used baking soda to raise, 1 plant was at 5.4 i like 6.2 so useing bakeing soda bit by bit raised ph back to 6.2 and let the plant alone till it dried, then i hit it with one more dose of Bloombastic, anyway it was a late plant around 85 days from sprouts but in the end it came out fine, white vinegar will lower ph or you can go buy ph up down, buy a nice electric ph meter it makes life eaysy, and there cheap i think i had a nute build up.

 

[JadedMarxist]

I've found that when my pH starts to go lower (which is opposite of what the ph should do) is when I start to up the enzymes. I found from experience that usually start of root rot or brown slime drives my pH down fast too try spraying some h202 3% directly into the roots see if they faom up like an infection.

Yes I have sprayed strait 3% h202 onto my roots and plant without damage.