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Coco Article

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Carl Carlson

Another misconception I have commonly encountered is that by measuring the run off (waste) in coir it is possible to measure the pH of the medium. Let’s quickly dispel with this myth. Coir media will retain some elements and release others (a process of preferential retention of cations) based on the uptake needs of plants and the prevailing conditions of/within the media.

Because of this, measuring the run off (waste) will not reflect the pH within the coir medium (i.e. the rhizosphere environment of the plants).

I agree with the author that this one needs to be put to bed for good.

Coco substrate is coco substrate and soil is soil - the two very different products require two very different treatments/approaches to realise optimum yields.

OK, so let’s put that aside; coco substrate is a hydroponic medium. Soil is soil. That simple!

He doesn't mention that coco can be used to amend or as a base in organic soilless mixes too.
 
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coconaut

I agree with the author that this one needs to be put to bed for good.

Have you run a recirculating system?
I do, and I can clearly see the author is wrong in his statement. I measure runoff, I also measure what's going to the pots. They do reach equilibrium.
The author mentions cations, he says "Coir media will retain some elements and release others based on the uptake needs of plants" This is laughable, as if coir knows what species of plant is planted and tailors a diet to suit that plant. i don't think so.
All medias have some level of CEC (cation exchange capacity), coirs capacity is just higher than other.
This CEC is like a matrix or 'net' within the coir. If this matrix is empty, it will grab ions out of a solution as the solution passes through the coir. The runoff solution will therefor have a lower EC than the input solution.

If the 'net' is full, and you pour a solution through the coir, some ions will be displaced from the 'net', and ions from the solution will replace those that have been displaced.
As more and more solution is applied, eventually the matrix will resemble the input solution.
 
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Mitch Connor

I'm glad I ran across that article after the first time I used coco. It definitely helped me tweak my methods and learn the ins and outs. Especially the section on pre-charging the coco (I was not informed of this on my first run with Chronic, had some stunted growth the first month or so.)

What coconaut says has validity. If you are running a drip-to-waste or any other system where the coco is being constantly saturated, the runoff will closely resemble what's in the medium.

If the medium is only being, lets say, hand watered once a day or once every 2 days for some plants, I've noticed that the runoff pH can be quite different from the input solution. I suspect this is the case because of what coconaut has stated about his "net" reference.

Some users of coco think it is beneficial to let the coco dry out a bit in between waterings to promote root growth. I agree with this statement to a degree. But, if you practice this method, make sure there is ample runoff coming out before you test. 3-5 minutes after the runoff stops, add a little more solution, then test THAT runoff to get as close of a reading as possible.

I'm going to be helping a friend build his own stealth cab very soon. I've instructed him to go over this article and absorb as much reliable coco info as possible.
 
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Carl Carlson

Yes and I should have been more specific and written that for drain to waste grows, the idea of measuring the pH of the medium by measuring the pH of the runoff from watering with nutrients, should be put to bed for good.

All medias have some level of CEC (cation exchange capacity), coirs capacity is just higher than other.

Perlite, rockwool and sand come to mind. I would treat them as if they have no CEC.
 
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