CEC.. If you do a little reading/research on the cec of coco, it will answer a lot of your questions. Non buffered coco has very little nitrogen in it. It does have an abundance of sodium(salts) and potassium. Nutrients dont just leach out during run off.. Coco excels at holding onto/retaining nutrients thru cec. If the coco is not/was not buffered, you could easily be dealing with a lock out. My guess would be either salt build, up or potassium excess.. An excess of potassium will lock out Nitrogen, calcium and magnesium.
This is a write up from Bonticare's web site. It will help shed some light on how coco works.. It helped lead me to many other articles on the subject. After months of reading and questioning, I feel like I have a completely different view of coco and how It works. I dont use it anymore because it doesnt really fit my grow style, but understanding how it works and why has helped me over all as a grower.
From Bonticare...
"One reason the coco coir is a popular growing medium is that it has a good cation exchange capacity (CEC) rating. Cations are positively charged ions such as calcium, magnesium, potassium, and sodium (among others), and the cation exchange capacity of a growing medium describes how well it can hold and exchange them. One way to think of a CEC is a rating of how well a medium stores nutrients.
Since coco is pretty good at holding nutrients, it should be of no surprise that it naturally has some attached to its cation sites. Specifically it starts with high levels of potassium and sodium.
Quality coco coir has been treated to replace some of these cation sites with a calcium (such as calcium nitrate). Calcium has a stronger bond to the cation sites than potassium or sodium because it has a double positive charge as opposed to the single positive charge of potassium or sodium.
This is done because untreated coco coir, being high in potassium to start with, will exchange nutrients in the nutrient solution and release potassium and sodium when used. Not only can this create an issue with denying the plant the intended solution, but it will release an overabundance of potassium. This can not only lead to a magnesium deficiency as described above, but the issues associated with potassium overdosing. By rinsing the coco coir with a solution of calcium before use, much of this issue is corrected. Coco coir that has already been treated is referred to as “buffered coco coir”.
By understanding the interaction between coco coir and plant nutrients, it becomes apparent that buffering is an important step in getting reliable and consistent results from coco coir use."
This is a write up from Bonticare's web site. It will help shed some light on how coco works.. It helped lead me to many other articles on the subject. After months of reading and questioning, I feel like I have a completely different view of coco and how It works. I dont use it anymore because it doesnt really fit my grow style, but understanding how it works and why has helped me over all as a grower.
From Bonticare...
"One reason the coco coir is a popular growing medium is that it has a good cation exchange capacity (CEC) rating. Cations are positively charged ions such as calcium, magnesium, potassium, and sodium (among others), and the cation exchange capacity of a growing medium describes how well it can hold and exchange them. One way to think of a CEC is a rating of how well a medium stores nutrients.
Since coco is pretty good at holding nutrients, it should be of no surprise that it naturally has some attached to its cation sites. Specifically it starts with high levels of potassium and sodium.
Quality coco coir has been treated to replace some of these cation sites with a calcium (such as calcium nitrate). Calcium has a stronger bond to the cation sites than potassium or sodium because it has a double positive charge as opposed to the single positive charge of potassium or sodium.
This is done because untreated coco coir, being high in potassium to start with, will exchange nutrients in the nutrient solution and release potassium and sodium when used. Not only can this create an issue with denying the plant the intended solution, but it will release an overabundance of potassium. This can not only lead to a magnesium deficiency as described above, but the issues associated with potassium overdosing. By rinsing the coco coir with a solution of calcium before use, much of this issue is corrected. Coco coir that has already been treated is referred to as “buffered coco coir”.
By understanding the interaction between coco coir and plant nutrients, it becomes apparent that buffering is an important step in getting reliable and consistent results from coco coir use."
