Rapid pH fluctuation issue

Hi all!
I am growing 2 White Siberian by Dinafem and 1 Bruce Banger by Seedsman in a RDWC system (3 sites + res - 5gal each). Im in week 5 of bloom and i am struggling to keep my pH stable. I am feeding Advanced Nutrients Sensi Bloom (A and B), B-52, Big Bud, Bud Candy, Rhino Skin + CalMag Plus and 2ml/gal Hydroguard. My current TDS is about 1200. Temperature at lights on never go above 79F and Humidity sits between 45 and 50%, my dissolved oxygen levels are about 2.6ppm mg/L.

I am having a very hard time controlling the pH. Roots are fine, i have a water chiller and the temp sits at 67F, no slime no smell. pH would rapidly increase in few hours from 5.5 to 6.5.

I do know that this can be indication of the plant being hungry, but i always fed at around 900ppm500 and just recently bumped it up since i start seeing Calcium issues.

Is there something i am missing here? Veg went smoothly as the first 4 weeks of bloom, nothing really changed, i assume its the plant trying to tell me something, just can’t figure out what, i would appreciate some new input, because at this point, after a week fighting this pH issue, i got nothing left.

Please let me know if more info is needed, this is my medical garden hence very important to me!


It’s a bird! It’s a plane! No it’s super @WickedAle!!!

That’s who comes to mind for me to give you excellent advice!


Hi! thank you for the response.

I do a res change every 7 days and my res was changed just yesterday, at the moment it seems like it has stabilized a bit around pH 6.0, i will include some data that might be beneficial below.


Thanks again!

Thank you!

The first spike in PPM was me changing the res, the second spike was me adding 100ml of CalMag to the res (20gal), which i forgot to mix in (yikes). The pH spikes with a downward trend its me pH down the solution, no need for pH up, the trend seems to always be upwards for pH. And yes, nutes are liquid, they are supposed to be “pH perfect” (yeah right?!) :slight_smile:

Edit: i also always mix nutes in this order:

  1. Rhino Skin (Silica) (i let it sit 1 to 3 hours and let dissolve)
  2. Cal/Mag plus
  3. Base nutes
  4. Bloom boosters and Humic acids
  5. Hydroguard
  6. Adjust pH

Hope this helps!

I do not calibrate the pH probe at every res change, but this is a fairly new Atlas Scientific industrial probe (2 weeks old), spoke to the manufacturer and they said that probes are calibrated from factory and do not need to be calibrated very often, no air bubbles in it, i also have an Apera pH meter (calibrated last week) and they read at the same value.
I knew that too about AN this is why i picked it, but after mixing nutes and letting it sit for half day pH was 6.7, so i had to pH it down.

This to me is a mystery! Never had this kind of issues before :frowning:

Probe is fine, measured solution at 4,7,10. Spot on for all measurements, been monitoring the pH, so far seems to have stabilized at 6.1 (the way i calculate is by taking 7 measurements, removing highest and lowest and calculating the average between the 5 remaining measurements), will see at lights on how they look.


I think 6.1 should be okay for them to start intaking Calcium

Thanks for the help!

It has been a very fast pH drift for the past week (from 5.5 to 6.5+ in few hours), until, the other morning i just decided to go for it and upped my nutes from ~900 to ~1250 PPM(500), i have applied since then couple rounds of pH down, multiple application of the solution seem to have slowed down the drift, but its still going up, if my math is correct i would have to apply pH down again by the end of the day (if it keeps this steady pace)

I use AN. I pH my water to 5.8 ish on a res change. After I add the nutes the pH is closer to 6.3 or 6.4. I add pH down to get it back to 5.8 ish. Next day pH is back up around 6.0. After one final round of adding pH down the increase slows down a bit but will still slowly increase. I’ll have to add pH down more time then it’s time for a res change.
I always thought this was because I use well water and the alkalinity is quite high. Could be that AN is buffered higher also.
This didn’t cause me any issues. Just finished my first grow and got around 18 ounces from two plants and one was a runt.

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@AI-warrior love your data display. Question, is that dissolved oxygen a real value? Seems low. Mine runs closer to 8 ppm.

@GoneFission Thank you and sorry for the late reply, apparently i sent “too many replies for a new user” and locked me out for 19hours…interesting!

It seemed extremely low to me too, this was a very new sensor i just got couple days ago, now its calibrated properly. The true reading now is 11ppm mg/l

As far as the issue, i think i simply locked them out! Way too much fertilizer, i brought everything down to ~600PPM, pH has stabilized, i left them overnight at pH 6.3 (to correct that Cal deficiency i was seeing) and so far its still at pH 6.3 and PPM have slightly increased ( ~60PPM), water level seem to be falling, but a slower rate.

I think i will just do a 12hrs flush with just RO water than mix everything again down to 500/550 PPM and see how they respond, after all seemed to be just overfeeding (hence the dark color of the leaves), this brought them to lock out (hence the Cal def)…

I should have known, deficiencies + burnt tips usually is nutes lockout.

Hope this helps someone else too!

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@GoneFission @WickedAle Pictures of the plant:

I think you’ll be fine. Sounds like you have it under control. These girls are tough. I went from this

To this

I wish I had your instrument setup. It’s what I’m used to at work. I work in Chemistry at a power plant. I’m jealous.


Wow! Bounced back amazingly! I agree, the data logging system gives me a lot of insights, really makes the plant speak to you!

I will keep you posted on the progress and thanks for the support!

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Maybe someday you can fill me in on your system. No rush. I’m more curious than anything.

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Sure thing, it’s 90% custom code, i have only used an open source front end to make it look pretty without having to waste too much time (I’m not a front-end person), but everything in the back-end is python, sweat, blood and tears. Well maybe not blood and tears, it was actually a fun project!
I am not sure if i can send private messages, but feel free to contact me if you want to geek out a bit!

Little update, bringing the solution down to ~600ppm seems to have done the trick. They drank about 3gal of water in the past 8 hours and pH and ppm are stable, mystery solved i guess :slight_smile:

This chart was helpful:


This chart is awesome! I wish you were my neighbor😉

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@GoneFission i have figured out the issue with the AN buffer, i went to the store and bought 0ppm RO water, followed their feeding chart in the nutrient calculator section of the website (not the quantities on the bottle) and it pH perfectly at 5.8. So, the trick is to use RO water at 0ppm or very low anyway, the water coming out my RO system has a mineral bed to reintroduce some minerals. i bet that screwed with their super delicate “pH perfect” buffers…hope it helps!

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@AI-warrior That’s great news! Thank you for that update. I suspect that’s also my problem as I’m on well water which has high alkalinity. I’m planning on using RO water on my next grow. But, due to summer activities, I won’t be starting that grow until late August. No matter, I’ve got 8 jars full.

Little photo update, the girls seems to have stabilized, and they are doing pretty good!