Root zone PH dropping - help!

Hello,
I grow in amended coco coir, 60% coco coir 40% hydroton.
I use the heads formula General Hydroponics 6/9 micro/bloom per gal water.

I currently water 3 times per day, automated system.
First irrigation is 20 min after lights on, second is 4 hours after lights on, 3rd is 8 hours after lights on

approximately 20% runoff

My starting tap water ranges from 0 PPM to 50 PPM on a Blue Lab meter.
I have seen this problem many times in the past and I do not know how to fix it.
This specific problem seems to happen after about day 30 of bloom.

This particular run I am at day 31 and I just took 3 seperate runoff readings and these were the results: Input pH / ppm = 6.0pH / 650 PPM / 1.3 EC
Cultivar A - 5.0 pH 650 ppm
Cultivar B - 5.3 pH 700 ppm
Cultivar C - 5.4 pH 680 ppm

What typically happens when I have this problem is the ph will continue to fall into the high 4 range, the plants will stop growing, the hairs will turn brown, natural oils / smells will die off and lose their odor.

some advice I have seen in the past has been:

Use calcium carbonate to buffer the water (I dont know how to do this?)

Use citric acid and then potassium hydroxide in concert and quicky feed to the plants to re-establish the lost buffer

Pre-buffer the starting water before adding nutrients via calmag or ph up to approximately 100-150 ppm


What I would like to know if anyone has seen this problem before or has corrected it and any suggestions.
Thank you in advance!

damn your tap looks like a giant RO system
you lucky lol

i think thats the origin of your problem

since youre not overfeeding, so the ph drop dont comes from there

i think your must buffer your water yes, until you get 200ppm minimum. with calmag for sure

and when you make your nutrient solution, how much time do you wait before giving it to your plants ? i like to wait overnight till the ph stabilize. otherway the ph you see on the meter wont be the same 2 hours after

Once the water is made it is usually used immediately. The ph of the solution seems to stay rock solid over the course of 2 days

Are you able to do a test of the coco pH on its own? as its known to have pH down to 5.2
This may also be useful regarding Cation Exchange Capacity: https://www.hill-laboratories.com/a.../CATION-EXCHANGE-CAPACITY-BASE-SATURATION.pdf - particularly pages 2 & 3.

This thread is a re-post

Original thread with two pages of answers: https://www.icmag.com/ic/showthread.php?t=359675

@jkd thank you I will look at that! Unfortunately I am unable to gather a remarkable quantity of the substrate for testing as it is all permeated with roots, I might be able to gather 50-100 ml of material from the top surface

@f-e yes I tried out this approach of multiple posting to see which thread got the most traction. I also posted on a couple other sites. I've found that sometimes posts go completely dormant while others are popular.

Rule number 2 of icmag

Duplicate postings with identical or similar text are not allowed. Duplicate postings will be removed

Click to expand...

romanolescro said:

damn your tap looks like a giant RO system
you lucky lol

i think thats the origin of your problem

since youre not overfeeding, so the ph drop dont comes from there

i think your must buffer your water yes, until you get 200ppm minimum. with calmag for sure

and when you make your nutrient solution, how much time do you wait before giving it to your plants ? i like to wait overnight till the ph stabilize. otherway the ph you see on the meter wont be the same 2 hours after

Click to expand...

I agree with Romano, I believe it's your tap water, what a wonder problem to have, my tap is 800 plus.

I spoke with the folks at Canna when I first began growing in coco, they recommended I add tap to my RO (5 ppm) to bring the ppm to 120 ppm. I don't like my tap at all so I use Epsom and Cali/Magic. I run reduced rates of Canna A&B so using these two products gets me to my desired Cal/Mag numbers.
The pH of my solution rises gradually and I let it roam from 5.8 to 6 before I readjust it. Can usually get two days watering's before I have to readjust.
I, like Romano, make my mix up after the last water cycle for the light period, 9 PM to 9 AM. I am in my 2nd week of flower. So at 7:45 AM after the last water cycle, I add upwards of 18 gallons to the rez, add the nutes and additives. The only difference between Romano and myself is I let the nutes stabilize for 12 plus hours then I pH about 30 minutes prior to first water cycle.

@romanolescro, does pH'ing right after you mix your nutes not get off track while the nutes stabilize? Would really like my pH to stay stable till the rez needs filling again.