Coco Coir - Low Rootzone Ph - Stopping Growth

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!
 
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Even though this was a few weeks ago and the grow is probably almost done... I'll take a stab at this for future reference, but I'm not a coco expert so take this with a grain of salt. Hopefully others will give their 2c..

Coco has a lot of K and therefore needs more Ca at certain times and can get depleted of it pretty quick, and once it loses the buffer the media ph will start to drop. The plants seem to be feeding though based on your numbers, they're probably hungry for Nitrogen since Calcium is an important mineral for N uptake.

What I would do is use about 100ppm of calcium Nitrate in addition to your nutrients for a few feeds and then taper it off. You wont want too much in there during late flower.
 
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I know one thing that if rootzone is acidic there is very likely a root rot. When roots die they produce lots of acid. Not saying this is the case, but something to keep in mind.
 
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
Drop your feeding to (2) times a day, Water them but not wash or soak them, if the ph is low then up the intake water ph to around 6.4 for 3-5 days until runnoff is back to normal range. Also see if they are feeding what you give them. Lower the nutrient intake if you need to.
 
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