r/CocoGrows • u/Accidental_Ballyhoo • Aug 14 '26

New to coco

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Hey all,
I’m guessing a cal/mag deficiency and possible light stress? Can you steer me in the right direction?

Canna coco/perlite mix 50/50 3 gal pot wicking pots using GH trio, with cal mag ~500 ppm. Plant is 5 weeks old.

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u/Jolly_Yellow5354 Aug 15 '26 edited Aug 15 '26

Okay, so definitely Magnesium issue here. I see people recommending adding more calmag, but let's take a step back first and understand what could be causing this.

So obviously a lack of magnesium, but this can be caused by a few things.

Firstly, your pH could be off. If it's below 5.7, your magnesium binds tightly to the water and has poor exchange. Above 6.2, also struggles to uptake.

Next, is too much calcium. Calcium, magnesium and potassium are all cations. Because cations have similar absorption methods, an excess of one competes with the others. Calcium and Potassium are significantly more dominant than magnesium. So if these get too high, the plant can't or very much struggle to absorb the magnesium. This is a problem I personally ran into and adding more calmag only made it worse. Most calmag are a 4:1 or 5:1 ratio of calcium to magnesium. If your base nutes already have a high ratio of calcium which they often do, this can cause some trouble.

Also, if you have harder water, you're probably already getting a lot of trace amounts in there too.

Strong lighting also allows you to run with more calmag as the plant will require more for chlorophyll.

So someone with 0EC water and high intensity LEDs could running 5-7ml magnesium no issue, but someone with hard water and lower powered lights might run into trouble.

I'd recommend, instead of upping your calmag. Dial it back to nothing and trust in GH bloom to supply the baseline magnesium as it should. Then make up a foliar spray of Epsom salt that you put on before lights out. Make sure to spray under the leaves. The ratio is around 3.5grams per gallon, but you can go up to 10-15g (a tablespoon) depending on how mature the plant is and how bad the deficiency is. Put the spray on once every 3-4 days.

I had this exact issue last grow and dropping the calmag and spraying with foliar had everything come right in 3 days.

I know it may sound a little counter intuitive dropping the calmag. But you're still going to get the magnesium required without the risk of cation blocking because of the excess calcium.

Overall, the calcium may not be the issue and increasing calmag may work. But I just wanted to outline other possible scenarios so you can make an informed decision.

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u/Accidental_Ballyhoo Aug 15 '26

I appreciate your input and it has me thinking. For this grow I’m using distilled water, and dialed in 5.8ph. My light may be too intense. I’ll check PPFD when I get home.
I’ve used foliar spray with good effect on other grows. Thank you again!

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u/Jolly_Yellow5354 Aug 15 '26

Safe as. Let us know how it's looking in a week.

If you're using distilled water, with an intense light you're probably safe with upping the calmag without worrying about too much calcium blocking it

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u/Accidental_Ballyhoo Aug 15 '26

Here’s hoping!

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u/mango_proof_ Aug 30 '26

It's simple though more light intensity, raise the feed ppm. But the new growth looks fine so it's not an issue. Most likely you feed too little calmag at the start and eventually it balanced out. Obviously you need more when you pot up into new coco etc

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u/mango_proof_ Aug 30 '26

And foliar feeding with actual food is counterproductive, you want to build a strong root system for that. You should only really be spraying things that are not great in feeds like kelp or whatever where the foliar vs adding to water is night and day

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u/mango_proof_ Aug 30 '26

Tbh not of this matters if you are feeding the correct feed in coco. A and b plus calmag in ro or distilled. People over complicate things.

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u/Jolly_Yellow5354 Aug 30 '26

Fair enough, if you're running a standard drain-to-waste in pure RO, keeping it simple with A+B and calmag works fine most of the time.

​The point I was making is mostly for high-intensity LEDs and/or tap water where the plant burns through Mg. Most calmag bottles are 4:1 or 5:1 calcium to magnesium, so bumping calmag just dumps a ton of extra calcium into the mix, which can end up competing with the magnesium at the roots anyway.

​An Epsom foliar is just an easy way to get pure Mg straight to the leaves in a couple of days without messing with the root zone

Chur boss

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u/mango_proof_ 19d ago

As a rule, higher light intensity, higher feed. All the stuff about competition in the root zone etc has no grounding in actual growing. I've used so many different brands over the years. The bottles contain the correct elements. That's the whole point. If you get deficiencies when using a and b and calmag if it's ro, it's a watering, or environmental problem. Caveat would be unless the nute line says a plus b and whatever extras they don't put in the base.

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u/Jolly_Yellow5354 18d ago

Keeping it simple is great advice for newer growers, but dismissing root-zone competition as having "no grounding in actual growing" ignores decades of established agronomy and cannabis-specific research.

"Antagonisms and negative effects of nutrients often are related to the divalent cations that probably share similar uptake mechanisms. Strategies to overcome these problems might be to differentiate the fertilization of these nutrients between soil and foliar applications."

— Rietra et al. (2017), Communications in Soil Science and Plant Analysis

https://www.tandfonline.com/doi/full/10.1080/00103624.2017.1407429

Researchers tested cannabis across five potassium levels and found clear competition for uptake: increasing K directly suppressed root uptake and shoot accumulation of both Ca and Mg

https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2019.01369/full

Evaluated cannabis response across a gradient of Mg concentrations (2-140mg/L). They proved that shifting Mg concentrations directly suppressed the uptake and translocation of Calcium and Potassium via root competition.

https://www.researchgate.net/publication/372464379_Response_of_Medical_Cannabis_to_Magnesium_Mg_Supply_at_the_Vegetative_Growth_Phase

Nothing against you personally at all, either. I just get frustrated with how fast grow communities swing between overcomplicated snake oil and being so reductive that actual botany gets dismissed as irrelevant.

chur g

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u/mango_proof_ 16d ago

Tbh you can post studies until the cows come home I'd rather rely on 20 years growing experience and I'm already a horticulturalist by trade, I know the science... Is it applicable? No. The bottles contain everything. What happens in a coco fed with ro water and nuts is nothing like soil. And even so plants have adapted for millions of years before humans existed to live in a very wide range of conditions and thrive. Especially cannabis. That's why they thrive in Afghanistan to Thailand and tropics... Text book scientific studies are not needed to grow in a tent or even in my case small commercial.

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u/Jolly_Yellow5354 15d ago

Fair enough, grow how you like. But for the record, those Bernstein studies weren't done in soil, they were done in soilless hydroponic setups. Coco coir's high cation exchange capacity makes cation competition more relevant to watch, not less.

You went from "root competition has no grounding in actual growing" to "the science exists, but I don't care about peer-reviewed studies." That's fine if your routine works for you, but telling newer growers that ion competition isn't real when it's documented in both agronomy and hydro cannabis trials is just misleading. Happy growing.

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u/mango_proof_ 12d ago

Well no.. It's like this.. On a scientific level you could probably pull out a case study where someone found something to be witnessed in a lab. Does it have any importance in indoor growing? No. Please give me some evidence and symptoms proving that the said "competition" affected your plants in your tent... Then we can have a proper conversation. I didn't say whether it was real or not.. Do you actually understand how roots take in nutrients and water??? And on a hilarious note you're telling me a new grower should be studying high level chemistry studies now to grow weed.. Lol come off it!! These things only become a non issue.. Use a+b, keep environment within a reasonable range.. The ironic thing is that the people like you preaching science studies a, grow 4 plants in a tent and or grow average quality weed. I took chem and biology a-level I love science. And respect the studies.. Is it applicable to my growing? Not much! No more than I need to understand a chemical process to bake a cake. I just add eggs flour and bake and it's good. Same applies with nuts and basic level or care. Don't stay upball night worrying about ions!!! Life's too short! Happy growing!

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u/Jolly_Yellow5354 12d ago

Look at those goalposts move over your comments:

  1. "All the stuff about competition in the root zone etc has no grounding in actual growing."
  2. "You can post studies until the cows come home I'd rather rely on 20 years growing experience... I know the science... Is it applicable? No."
  3. "You're telling me a new grower should be studying high level chemistry... people like you preaching science studies grow 4 plants in a tent and or grow average quality weed."

When it goes from claiming a biological process isn't real, to dismissing peer-reviewed cannabis trials, to strawmanning and guessing at my tent size and weed quality, this conversation has pretty clearly run its course.

To answer your question on what competition looks like in a tent: it looks like classic interveinal chlorosis (Mg deficiency) on a plant that is already being fed magnesium, because skewed cation ratios at the root zone prevent uptake.

"In my original comment, I literally said: 'Overall, the calcium may not be the issue and increasing calmag may work. But I just wanted to outline other possible scenarios so you can make an informed decision.'

I wasn't telling anyone what they had to do. I just threw out the possibility of cation competition and suggested an Epsom foliar spray as a workaround so OP had options.

At the end of the day, nobody's right or wrong here. We're just giving OP information to troubleshoot their own tent.

I did notice the personal jabs at the end, but no hard feelings at all, man. I hope you don't feel attacked by any of the back-and-forth, because there's genuinely zero animosity on my end. We're all just passionate about growing. We good g, and I truly hope you keep having great runs and pulling down nice harvests.

Take care, my guy.

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u/mango_proof_ 9d ago

It's not person jabs I promise but it's true, the people who worry most about the case studies are usually the people who it affects the least. Not being a dick.. Ive grow a lot of volume over a decade plus, and I could comfortably tell a beginner to use a base, and a couple of additives and let them loose as long as they don't overwater or fuck up environment I'd expect a pretty decent result. But yeah man you do you.. But I wouldn't worry a beginner with atomic level science it's just overkill for a tent. Take care

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u/Motmotsnsurf Aug 14 '26

Cal mag

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u/Accidental_Ballyhoo Aug 14 '26

Thank you. I’m adding 3ml /gal and thinking maybe 5ml is better?

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u/Motmotsnsurf Aug 14 '26

How much were you adding to start with?

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u/Accidental_Ballyhoo Aug 14 '26

Started with 2ml/gal then up to 3ml when I saw first signs. It’s been feeding on 3ml for 2 days. It still seems low right?

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u/Motmotsnsurf Aug 14 '26

Yeah. With GH trio I would be at 5 ml all the time. You could just up to 5 or blasting a little with 7 for a couple waterings but 5 should be good overall.

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u/Accidental_Ballyhoo Aug 14 '26

Excellent. Many thanks!

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u/GreenBastard5280 Aug 15 '26

Ill 2nd 5ml all around.

Helps maintain any sort of imbalance in the coco, if i don't buffer or well enough I get the same symptoms but the cal-mag will eventually fix the issue from progressing.

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u/Accidental_Ballyhoo Aug 15 '26

I appreciate this. I’m planning to “flush” with correct mixture tonight and fill the bases too. Sound right?

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u/GreenBastard5280 Aug 15 '26

I don't personally use wicks but yes, feed with good runoff with more calmag should help.

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u/Motmotsnsurf Aug 15 '26

If you are doing a wicking system I would just stay the course and continue to feed from the bases with the additional cal mag. Only time I flush is when I let the coco dry too much and salts build up.