Hi everyone,
My 2cents to this thread...
I believe coco coir is taken way too seriously regarding cation exchange capacity. Growers get overly absorbed about it.
The fact of the matter is, its coconut husk. It NATURALLY contains very high amounts of calcium, magnesium, potassium, and sodium. (It grows and is processed on, or near the beach)
Also the material is organic. (it is continuously composting and breaking down. Just like soil.)
Because it is continuously breaking down, then it leaches, or excretes these salts from itself. This is Cation Exchange Capacity. (just like soil)
It also has the ability to absorb water, and dissolved solids like a sponge. (just like soil)
The issue with coir is the sodium content. The levels are very high, and very quickly turn into lockout, and deficiency issues.
This salt NEEDS to be dissolved, and leached from the coir. This is generally the inherent problem with buying block coir. Also some coir is much greener, (fresher) than they should be. It needs to be aged. Most husks just get thrown through a wood chipper. Some are processed greener than others. The greener the coir, the more sodic it is.
They have to be expanded, and leached properly. Otherwise it causes a whole heap of problems. Typically 99% of the time calcium and magnesium deficiency, potassium toxicity, and extremely low osmosis to the plant. (we see it ALL THE TIME here on RIU)
They look extremely droopy, dry, malnourished, wilted, blistered, and thirsty. All at the same time.
Using lime to "buffer" your coir, in this case will not only catch the sodium, and cause sodium to remain in the media. But it will raise the ph as well. Its counter productive to what we're trying to achieve. (sodium scarce root zone)
Personally ive only ever limed my coir once, which was on my first coco grow.
In my own experience it is far easier, to stick with a synthetic nutrient. Because the solution has the ability to pass through, and be absorbed by the micro fibres in the coir. (its porous, and extremely absorbent).
Personally i never pre buffer with calmag. I only rinse it with my base feed, and buy block coir. I have never bought a bag of pre expanded, and prepared coir.
In my opinion it isn't true about needing extra calmag, less potassium etc, etc. My own NPK right now comes to 6-4-10. This ratio hasn't changed since seedling stage. Only the strength.
The "Cation Exchange Capacity" isn't a complicated thing. Quite simply we water with our nutrient solution (which contains cations). The coir reaches saturation, then leaches what it is holding to the waste. Then absorbs the new nutrient solution (it exchanges).
The number 1 rule with coir, is to NEVER let the coir dry too much. Because otherwise the coir DOES rob the root zone of calmag etc, and starts "charging up". The trick is to never let this occurrence happen.
Coir is incredibly inert when kept moist. Holds an insane amount of air, and doesnt require perlite. Doesn't need buffering, because it buffers itself. Is extremely inert when saturated. Naturally holds a ph of around 6.5 to 7, also is mold and bacteria resistant.
Its an excellent DTW medium for these reasons alone.
Also whenever something isn't right with my plants in coco. I ALWAYS check my waste, and judge what to do from there. Every time theres something wrong, the waste ppms are either way too high. Or the ph is way out of whack.
This is so easy to rectify. Because all that needs doing is rinsing the media with our base nutrient. Until whats coming out in the waste is matching whats going in. BOTH ph and ppm. It is that simple.
I even germinate my seeds in coir. Always have.
There must be waste every feed as well. Otherwise buildup, and lockout definitely will happen.
Any lime or additives in our coir makes these processes much harder to achieve, or perceive accurately.
I'll include a couple photos to hopefully help explain my point.
Seeds broke ground on the 1st of July. First photo is from the 12th of July. Second photo is today. I'll include them as a thumbnail.
Peace to all.
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