Coco Coir - Low Rootzone Ph - Stopping Growth

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Fourtay

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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!
 
Dirtbag

Dirtbag

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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.
 
Shroomtrips

Shroomtrips

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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.
 
DesertHeat

DesertHeat

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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.
 
Last edited:
Herbz420

Herbz420

6
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Hey little old this post but i always have the same problems in coco. Two grows ago i added tapwater (calcium carbonate) and the ph was fine i got big yields but something was still wrong. The plants didnt smell very good and the roots were tiny and didnt look healthy.
Last grow i did not add tapwater and did sometimes a flush and the ph was fine for 2days šŸ¤£ and dropped again back to ph 5.0 and the roots looked brown and very unhealthy the yields were very low this run but the plants smelled better/was the same plants from seeds i used last grow.
Would be great if someone knows whats happening here? I have some new seeds and the ph went from 6.0 to 5.7 in one week the roots lookin ok but could be better and i know the ph will drop like last grows to the point were the plants dont drink that much water.. The seedlings Show little wavy/crinkled leafs like last grows and after one to two weeks the plants show some brown points on the leafs, look like calcium deficiency but maybe the plants cant absorb the calcium because of root rot problems?

1. Maybe it is overfeeding that the ph drops in coco? The runoff ec is always the same what i put into.
2. Too much potassium from the coco and too little calcium? Potassium excess will drop the ph and if too much potassium is in the coco the plants cant absorb calcium.
3. It is root rot. But the roots look fine at the start and if the ph drops the roots start to look unhealthy.
What should i do if its root rot? Is Hydrogen peroxide a good idea? Last grow i used hydroguard and it did nothing. The temperature in the grow box are really hot like 24-26Ā°C and i cant bring the temps down because outside it has 30Ā°C.. And in the coco the temps are at 24Ā°C.. Too high but i dont know how to bring the temps down if this is causing the root rot or the ph drop in the coco.
Sorry for the bad english and hope someone knows what i should do or how i can find out whats causing my problems.
 
Aqua Man

Aqua Man

26,480
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Your cal mag might have calcium but that doesn't mean it's calcium carbonate. It is the carbonates and bicarbonates that buffer your ph. The more carbonates the higher the buffering capacity (ability to neutralize acid). Baking soda (sodium bicarbonate) will work as a buffer but ideally calcium carbonate would fit your situation. Typically potassium bicarbonate is used as ph up but sounds like calcium would be more beneficial in your circumstances. It will depend on how acid you water is as to how much calcium carbonate is needed. There are calculations to find this out but I never them and do things the lazy way. Take a measured amount of run off say a gallon and grab a scale and your calcium carbonate. Start with 0.1 grams and add to the runoff then stir until dissolved and the measure ph. Continue this until you reach your target ph and from there on you know how much calcium carbonate to add to your feed for the correct buffer.

Now this is a temp fix and I don't grow in coco but I would suggest pre conditioning your coco by soaking it in a buffer for a few days before using to eliminate this in the future. I have seen posts on this and other sites with directions of how to do so but never done it so I don't wanna give any advice on it.
 

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