Recurring problem with low ph in coco

Why You Need to Buffer Coco Coir

There are cation exchange sites in coco that will interfere with nutrition until they are buffered. The cation exchange sites in coco naturally come loaded with sodium (Na) and potassium (K) cations. However, the Na and the K are only weakly held to the exchange sites. In the presence of calcium (Ca) or magnesium (Mg), the sites will release their Na or K cations and lock onto the Ca or Mg. These processes are known as “cation exchanges”.
Buffering coco is accomplished by soaking it in Ca and Mg. This allows the cation exchanges to take place prior to adding plants. Simply soak your coco in a solution of Cal/Mag water and the exchange sites will release their K and Na cations and lock onto the Ca and Mg. When the cation exchange sites bond with Ca and Mg rather than Na and K, it is “buffered”. The bonds that hold the Ca and Mg to the sites are very strong and cation exchange will largely stop. This means that all of the nutrients that you add to the water will be available to the plant at the ratios that you provide them.
Growing in Un-Buffered Coco

Many growers are unaware of the need to buffer the coco and they try to grow plants in unbuffered coco. In unbuffered coco, the cation exchange sites will strip the nutrient solution of the Ca and Mg and replace those cations with Na and K. This creates a sub-optimal Nutrient Element Ratio (NER) and renders Ca and Mg unavailable to the plant.
Failing to buffer the coco is why so many growers suffer calcium deficiencies in coco grows. Manufacturers of prepared coco products try to exploit these problems and convince growers that only their proprietary products are suitable for growing. However, it is actually very simple to properly buffer your coco yourself. This tutorial walks you through the process and provides all the information you need to turn even the cheapest brick of dehydrated coco into a superior growing medium.

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Suntana said:

This is an old thread but good info. He has a few spelling errors to figure out lol

The Chemistry behind Coco Coir: a (strange) journey from ferts bottle to to buds

/ icon and title message
Growing is something strange as it can be as much complicated as you want. Beside that, some growing methods needs a better understanding of the involved chemical processes than others. Coco coir (in my opinion) is one of them.

"Coco Coir tend to adsorb Calcium and Magnesium", "pH of nutrient solution should always be adjusted to the correct value", "checking drainage ec and pH is also important" as well as "checking drainage pH and ec makes no sense as coco holds nutrients and modify pH", "Coco is an inhert media"or "Coco has high CEC" are only few exemples of how many confusing infos can be found on the internet.

If you haven't heard none of this rules before, you are likely to have never grown in coco or at least, you were lucky enough to not need search the web for hints and tips.

Some of those rules are true, others are not, but in most cases they're only simplicistic aproximations of reality.

So, are you ready?

Step 1, the basics: pH, salts and Ions (aka the good, the Bad, the Ugly)
"Daddy, why seawater tastes that baaad?"
"Ohhh it's easy my son, it's cuz there is salt in it!"
"Wow you know lot of things daddy, but what is salt?"
Bump! Panic "ehm, son, why dont you go play with your friends now? It's summer! Have fun!"

Encyclopedia, Salt: elettrically neutral chemical compound, made of 2 or more Ions with opposite electrical charge.

Lets take a look at the seasalt, almost everybody knows that its chemical formula is NaCl. In its solid form is a quiet stable compound, but what happens when we put it in water?
Correct, it dissolves, but what it means?
What actually happens is that salt divides in its Ions: Na+Cl-
If we want to be exact, there is no salt in the solution, its crystalline structure got dissolved, just positive and negative Ions. Keep those last word in mind and put them in a corner, we'll need them soon.
Everything clear till now?
Good, lets go ahed.

Water!
Water has many characteristics, almost everyone quite unique. But when the talk is about Ions, two becomes particullary important: water is an amphoteric and polar compound. Lets start from the last one.

While the term "polar" could suggest something related to cold places, it actually referres to magnetic/electric poles. Saing water is "polar" simply means that its molecule is electrically asimmetric. Everybody knows water chemical formula is H2O and if you don't, please, pick up a lighter and set your hair on fire for punishment.
So 2 Hydrogen atoms and 1 Oxygen, but maybe not everyone knows that its structure it's like that:



As you can see, water molecule has some sort of triangular shape, with the oxygen side been slightly (it all depends on the point of view) negative charged, and viceversa.
Could seem a little thing, but without this there would be no plants to grow.

Amphoteric is somehow a weird word. Anyway it basically means that water can act as an acid as well as a base. For definition, an Acid is something capable of releasing H+ ions, while a base is something that attract them. If put thogeter with someting more acidic, water will act as a base and viceversa

Pure water at room temperature is made of stable H2O molecules, but a really small amount "divide" to H+ and OH-

Beware that "divide" is not correct, is more of an addition:

2 H2O <--> H3O+ OH-

At the end of the day it's basically the same thing, we always have a H+ on a side, and a OH- on the other. From know on, please consider H+ and H3O+ as the same thing. In most reactions you'll see H3O+ cause it's the real form, while when talking we'll refer to H+ for easier reading.

Anyway, I sad "only a small amount". Guess how many? 1 every 10.000.000 or 1 × 10-7. Look at that "-7". Ever wondered "why pH7"? now you know.

As we have seen pH7 also mean that H+ and OH- are present in the same concentration.
If you use RO water, thats quite near what comes out from the blue hose

But if we put an acid in it, water will act as a base, bonding to an H+

H2O + HCl -> H3O+ Cl-

More H3O+ compared to OH- The pH is lowering. Ten times more H+ means 1 point less in pH.

Viceversa H2O+NH3-> OH- NH4+
More OH- compared to H+. The pH is rising.

So I've just said pure water has pH7 so same amount of H+ and OH-.
Oh, well, there's a last minute problem, like when you see there's only 10gr left and you're still in Veg: pure water is a great solvent, enough powerful to react with CO2 normally present in air to create Carbonic Acid.

H2O+CO2 -> H2CO3

Being H2CO3 an acid, water play its role as a base, actracting H+ from the newcomer and lowering pH till a 5.5 value.

Why till 5.5 and not more? I've said water act as base when toghether with someting MORE acidic. In that case, 5.5 is the equilibrium point. Maybe you are allready thinking that adding your pH+ would be a simple solution but think about it: if you raise the pH, water will be once again basic if compared to H2CO3, at that time will start to act as a base as before.

Seems frustating doesn't it? Well, actually it's a great thing: the fact is that water by its own has a very low inertia to pH adjustment. In other word, easily matches pH of surrounding substances.

Know you should start to understand why the amphoteric behavior is so important.

But what about polarity?

The answer is quite simple (or at least more simple than the amphteric thing): polarity enables water dissolve salts crystalline structure and idrate positive and negative Ions.

Look at the picture below:
Salts in a water solution are like you and your girl dancing in the middle of 1000's Bred Pit & Angelina Jolie straight in the middle of a 7th year crisys.

Few minutes later, the situation will likely be like that on the right



Now stop thinking angelina's green eyes for a while (yes I am a romanthic guy) and focus on female plants. Fertilizers are salts, but plants need them in their ionic form to be able to adsorb them.

Now you know what salts and Ions are, how water acts like, and what happens when those 3 are put togheter.

"Wait, but the title said pH, salts and Ions, not water, salts and ions!! What da f**k was that for??"

Well, pH is like balance between brads and angelinas. Too many Brad and only few Angelina will make them forget about the 7year crisys and try hard to reconquest the few remaining ledies. In three words: you are screwd.

If you kept reading till now, i'm quite sure you have seen this graphic before:



I'll not explain them one by one, but keep in mind that any significative change from pH7 could cause serius issues. As said before, 1 point more in pH means 10 times more OH- and 2 point more means 100 times more OH-, the opposite for H+ ions.

Roots use H+ and OH- to adsorb macro and micro elements, so pH balance in the nutrient solution is very important to make it possible. Beside that, different pH causes different equilibrium between ions, making possible reactions that doesn't happen under neutral conditions, resulting for example in unsolvable salts.
Undissolved salt means (quite) no ions, and no ions means no food for the plant.


So now you should have a clearer view of what happens when you mix those high quality ferts in water.
But in wich way plants actually eat (or maybe drink) them?
On a chemical level, two main things come in place: osmotic pressure and ion exchange.

Before we start there is a very important thing you must have clear in mind: everything in chemistry goes in the direction of maximum equilibrium or, if you prefer, maximum stability level.
Salts dissolve into Ions simply because, when put side by side to water molecule, that is the most stable form. If something changes (pH for example), also equilibrium point will, and things will start moving again seeking the new stability level.

Osmotic pressure and ion exchange makes no exception: they'r all about stability and equilibrium.

Osmotic membranes (like cellular membranes) are also called "semipermeable membrane". Basically, it means that they are able to let some molecules (like water molecules) pass trough, while blocking others (like ions).
At the same time, osmotic pressure is an intrinsecal chemical property of solutions. The lower the concentration of ions, the higher the osmotic pressure.
If concentrations, and for direct conseguence osmotic pressure, on the two sides of a semipermeable membrane (like root cells membrane) are different, water will be forced to move from the higher pressure side (low concentration) to the other (high concentration). Once the concentrations on the to sides are the same, so will be osmotic pressures: equilibrium has been reached. Under normal conditions, ion concentration inside root is higher than that in the nutrient solution, so water will be literally pushed inside roots trought their semipermeable membrane by means of osmotic pressure.

So, while water is somehow "pushed" inside plants, ions are litterallh captured by them.
We just said that water inside roots is quite rich in ions, and this is a key point. Some of those Ions are micro and macro elements that were already adsorbed, while others are simply H+ and OH- resulting from water dissociation.
Since like every Ion, micro and macro element ions in solution have their own electrical charge (K+ for example) plants can't just "take" them, otherwise equilibrium would be broken. What they actually do is swap them with equivalent amount of H+ and OH-

For exemple

potassium (K+) swapped with 1xH+
calcium (Ca++) swapped with 2xH+
magnesium (Mg++) swapped with 2xH+
ammonium (NH4+) swapped with 1xH+
iron (Fe++) swapped with 2xH+
manganese (Mn++) swapped with 2xH+
zinc (Zn++) swapped with 2xH+
nitrates (NO3-) swapped with 1xOH-
phosphates (HPO4--) swapped with 2xOH-

In this way electrical charge equilibrium remains the sama and at the same time, roots releasing H+ or OH- make pH fluctuate.
This is a well known behavior for hydroponic growers, where there is quite no buffering power in the media to oppose to this.
I said buffering? Keep reading...

Step 3, those damn colloids! pH buffering and Cations exchange capacity in coco coir

Coco coir is characterized by a quite high colloid content and therefore, good CEC or cation excange capacity.
Keep in mind that "Cation" is just another name for positive charged ions, so this basically quantifies the substrate ability to exchange positive charged ions (with nutrient solution as well as with roots)

Now, imagine colloids as big spheres with a negative charged surface. Being so big and at the same time having such a strong electrical charge, makes them able to bond to a very large amount of Cations (+Ions).
Even if electrical charge has the same "weight" between different ions (for example K+ and H+ or Ca++ and Mg++) Ions are still differently attracted by colloids. Many factors come in place like ions dimensions and steric configuration for example. Anyway, the most important one is still the electrical charge, so Ca++ and Mg++ are more easly abtracted than, for example, H+ or K+.
This is very important, and explains quite well why its common tought that extra Ca/Mg are needed when growin in coco.
I said common tought because, in fact, the plant need the same amount of Ca/Mg in coco as in other substrate. Its just a matter of fullfilling CEC.

So, we have seen that coco can retain some Ca/Mg beside other Cations as well, but is this GOOD or BAD?

The answer is neither one or another. In fact, coco acts as a buffer on nutes level. Once the CEC is fullfilled (for example by multiple feeding or, better, one night submerged in the nutrient solution), colloids will have reached an equilibrium with nutrient solution. In this situation, if we feed pure ro water, colloids will release cations, if we feed a very high ec solution, colloids will be forced to bond to more cations.

This is also true for pH buffering. As H+ is a Cation, colloids will abtract them in great quantity. If we feed high pH solution (lot of OH- and few H+), colloids will release H+ and viceversa. As we have seen before, its all about equilibrium.

So, its now clear that the most important part is correctly fullfilling its CEC. This can be easly achieved by letting coco coir sit in a balanced nutrient solution with correct pH level for some time (say, for example, a night).

This also mean that checking in/out ec is important too. Inlet ec higher than out ec means colloid are actracting ions, while inlet ec lower than out ec means colloids are releasing ions. This is a very usefull information about CEC in that specific moment and also suggests if corrections are needed.

Regarding pH, providing a nutrient solution corrected to the right value is not bad, anyway slight deviations from correct pH value will be at most compensated by the coco coir it self.

At the same time, tring to keep run-off pH at the correct value by changing pH input could do more harm than good. As we have seen before, pH fluctuation is a natural conseguence of ions exchange operated by plant roots. Beside that, having a substrate that also affect pH makes thing even more complicated.

At the end of the day, you should correct pH if your starting water has high ec (that means high Ca/Mg wich act as pH buffers). An high buffered water will make it more difficult for the colloids to bring pH to the correct value (as an high buffered water will need higher amuont of H+ ions to change it's pH if compare do low buffered / low ec waters).
Long cicles with such water at very high pH could, week by week, unable the substrate capacity of compensating pH (anyway this is a very rare situation)

Using ro water or tap water with medium or low ec (say <0,4) usually makes pH correction quite useless.
As we have seen, water without buffering ions vary its pH very easly so an incorrect value should be quickly compensated by the substrate.

Step 4: think think think

So, if you came here honestly, and you really red all that boring stuff up there, you shuold have already made your mind about what to do and what to avoid when growing in coco.

Any way, lets review the key points:

- starting water: the best solution is to use tap water if ec is <0,4 or slightly higher. With high EC tap wather, is really suggested to use a RO system, than cut RO water with tap water till 0,3-0,4mS/cm

- pH: if your starting water is like the one mentioned above, pH adjustment shouldn't be necessary. You can always adjust nutes pH but please, do not rise or lower it to achieve correct run off pH: it doesn't make any sense. Run off pH can fluctuate a lot due to roots activity, and that's absolutely normal

EC: of course you should adjust your feed EC to the right value. It's also very important to check for run off EC once a week more or less. Run off EC should be as close as possible to feed EC. If you find it lower or higher a good way to take it back to normal is to just increase your feeding time. For example, if you are feeding 2 times per 10 minutes each, switch to 2 times 12 minutes.

Feeding Times: you should adjust your feeding time to achieve a sufficient run off. That way you can assure coco CEC is always buffered while also preventing salts build up. You should also adjust number of feeding to let the substrate dry a bit between a feed and the other.

Pot size: best results are achieved with a pot size that enables you to give up to 3 or 4 feed per day when the plants are in the maximum need. It usually means quite small pots.

Perlite and clay pebbles: by washing your coco coir before seedling (remember the "fullfilling cec" thing?) you should also wash away all the finest dust so you end up having quite large fibers. In that situation, you really doesn't need perlite. If you're missing it, you should consider to

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f-e said:

One of the big drivers in alkalinity is calcium. Much of coco's buffering is calcium, which sticks well. If we don't give enough in the feed, the plants start to strip this buffering. When we feed again, a lot of our calcium won't run-off as it's stuck to the coco. The feed in suspension then has a lower pH. It's calcium re-appropriated. With RO this might be about the only thing that kept the pH up, so huge drops are likely. One user spoke of the toxicity seen at 5.3 from manganese and boron. At the same time a whole raft of things become unavailable. Many of which can reduce green production.

It's important in coco to keep up the calcium levels, and use some buffering from the tap. We should use some tap in any circumstance but that hard to access calcium carbonate is especially useful for buffing the pH in coco or hydro. Also, we don't see problems from people using too high a pH in coco. More commonly, RO users have a pH that looks high so they add acid, which wasn't needed. Tanks made up with low buffering will be at substrate pH almost on contact. Any acid added, it's useful. With nothing in your tank by RO and feed, what does the acid find to work upon? It's not going to play well.

Personally, I might use RO and feed, then not even look at the pH as it has no staying power once it hits the coco. To this volume of RO I might add 15% more from the tap. I'm looking for a bit of hardness to prop up the pH in the substrate. There are figures to target here, it's not bro science. 30-75ppm of hardness covers most situations. My tap is about 300, so if 15% of my tank comes from the tap, that's about 45ppm. I wouldn't care if it was anywhere between 30 and 100 while trying to figure it out.

Never wash your coco with just water. It removes the buffering. The next feeds will be robbed, putting it back. Washing coco is a setback. You just aim for more run-off. Never less than half feed, with just calmag being an option. There must always be something for the coco, or the coco's own K and Na will make good use of the cec sites. Then when you do add some Ca+Mg this K and Na will be displaced as they have a weaker bond. The result for your feed isn't good, having it's Ca+Mg taken and replaced with K and sodium. It's another setback.


Acidification from excess feed build up.
Acidification from excess acid
Loss of Alkalinity from not adding any
Bacterial action.
Loss of what did raise the pH, as it was eaten
Lowering of the pH through the consumption of some feed elements.
Lowering of the pH because your test equipment sucks...

I feed in the mid 6s, fwiw

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tw420good said:

Want to know the solution thank you

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f-e said:

One of the big drivers in alkalinity is calcium. Much of coco's buffering is calcium, which sticks well. If we don't give enough in the feed, the plants start to strip this buffering. When we feed again, a lot of our calcium won't run-off as it's stuck to the coco. The feed in suspension then has a lower pH. It's calcium re-appropriated. With RO this might be about the only thing that kept the pH up, so huge drops are likely. One user spoke of the toxicity seen at 5.3 from manganese and boron. At the same time a whole raft of things become unavailable. Many of which can reduce green production.

It's important in coco to keep up the calcium levels, and use some buffering from the tap. We should use some tap in any circumstance but that hard to access calcium carbonate is especially useful for buffing the pH in coco or hydro. Also, we don't see problems from people using too high a pH in coco. More commonly, RO users have a pH that looks high so they add acid, which wasn't needed. Tanks made up with low buffering will be at substrate pH almost on contact. Any acid added, it's useful. With nothing in your tank by RO and feed, what does the acid find to work upon? It's not going to play well.

Personally, I might use RO and feed, then not even look at the pH as it has no staying power once it hits the coco. To this volume of RO I might add 15% more from the tap. I'm looking for a bit of hardness to prop up the pH in the substrate. There are figures to target here, it's not bro science. 30-75ppm of hardness covers most situations. My tap is about 300, so if 15% of my tank comes from the tap, that's about 45ppm. I wouldn't care if it was anywhere between 30 and 100 while trying to figure it out.

Never wash your coco with just water. It removes the buffering. The next feeds will be robbed, putting it back. Washing coco is a setback. You just aim for more run-off. Never less than half feed, with just calmag being an option. There must always be something for the coco, or the coco's own K and Na will make good use of the cec sites. Then when you do add some Ca+Mg this K and Na will be displaced as they have a weaker bond. The result for your feed isn't good, having it's Ca+Mg taken and replaced with K and sodium. It's another setback.


Acidification from excess feed build up.
Acidification from excess acid
Loss of Alkalinity from not adding any
Bacterial action.
Loss of what did raise the pH, as it was eaten
Lowering of the pH through the consumption of some feed elements.
Lowering of the pH because your test equipment sucks...

I feed in the mid 6s, fwiw

Click to expand...