Is this a magnesium def.?

Autoflowers from various seed banks.
Indoor, 2x4 grow tent.
Medium: ~75% canna coco (buffered), ~25% worm castings + a bit of perlite thrown in.
Nutes: 3tbs/gallon of medium. Added 70% gaea green 4-4-4 & 30% gaea green 2-8-4.
Top dressed Dec. 19 with 2tbs/gallon of medium + more worm castings. 30% gaea green 4-4-4 & 70% gaea green 2-8-4
Source water: tap, ~7.1pH, <100ppm
Lighting: LED, 1x200W, 1x100W
Watering: pH’d then watered every 1.5 days
Plants sprouted between Nov. 15 & Nov. 17

Everything I see online says this is magnesium deficiency. I’ve been using calmag for over a month, adding every 2nd watering, package says 2ml/L so that’s what I’ve been following. I doubled the does at the last watering hoping maybe that will help? I’m also going to start using it every watering instead of every 2nd. Any suggestions?

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Are you PHing your water down to 5.8-6.0 The rust spots do appear to be calcium issue. I don’t grow in Coco so I’m probably not the best to give advice. Your girls look relatively healthy, aside from the rust spots. I’ll tag a couple of people to take a look and see what they think.

@AfgVet @MidwestGuy @BobbyDigital


I do pH it down to 6.2-6.8. I try to vary the pH within that range every watering. I am following Mr Canucks Grow and that’s what he does for this type of Coco mix. In a previous thread I had noted some problems and at the time I was pH’ing down to 5.5-6.0 however oldmarine said he considers it using coco in your soil rather than a coco grow so to pH to soil levels rather than if you’re using pure coco. Anyways it seemed to fix the problems I was having at the time so I just carried on with it.


OK, it appears that it’s a calcium issue. I grow in soil and start cal-mag within the first couple of weeks. Full strength .5ml every watering. Let’s see what the others that I tagged think :+1:


I’m also a soil grower, so not sure how much I can help, but I’ll ask what the relative humidity and temperature is in your grow space? They look pretty well fed, so one (of many) possibilities is high humidity. Calcium doesn’t move through the plants very well if the humidity is too high in relation to the temperature.


Problem with your mix is; it’s not soil and it’s not soilless. There are a whole bunch of micronutrients present in soil that you do not have in your mix. Gypsum is usually added. Or dolomitic lime which is then available to the plant.

Unless you are an expert in soil building I would never suggest doing your own.

Plants appear to be hungry more than anything.

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Over the past few days temps have ranged from 67-75. Humidity is 48-93. I am running 6 on 2 off light cycle. My exhaust fan doesn’t have temp/hum. controls. I found if I leave it on while lights are out the temp drops significantly. Having it go off with the lights is what runs the humidity up but it’s only for a short time. It takes about 15 mins for it to get back down into the 50s once the lights come on. Since the lights are only off for 2 hours I wasn’t sure if a short duration of high humidity would be a problem. I recently acquired an infinity that can be controlled by temp & humidity so I am going to set that up soon.

So I have a post saying they look well fed, and right below a post saying they’re hungry. Hmm…

Regarding the soil, I am following what Mr Canucks Grow did and it seemed to work well for him. foward to 6:25 to see the mix. I have not had much luck with soil, between living soil that seemed to cause nute burn and other various mixes in which I’ve had big problems with pests. This stuff has been wonderful to work with. No a single sign of pests.

So this is what the worm castings have, I assume it addresses the missing things you’re suggesting:

All natural, odorless and non-toxic
Rich in humus
Improves soil structure and aeration
Contains essential plant nutrients and beneficial micro organisms
Demonstrated fungicide and insect repelling properties
pH neutral
Adds beneficial micro organisms for pathogen control
Increased plant growth rate
Contains vitamins, enzymes and plant growth promoters such as auxins and Gibberellins
Safe to use on annuals, perennials, seedlings, cacti and succulents
Significantly cuts your fertilizer inputs
Excellent water retention which substantially reduces irrigation
Free from harmful pathogens and contains beneficial organisms to protect against disease
Will not wash out with watering

I’m still experimenting to find a medium that works for me. This is my first run with it but I like it so far.

Definitely follow advice from @Myfriendis410 over anything I told you.

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Here is a shot of the entire canopy. If you still feel they look hungry I’ll give them another top dress. Was planning on it a week from now but if they’re looking for food already I should give it to them.

It would be good to get a runoff TDS to see what salts are present in your media.

Worm castings are good stuff and you almost can’t give the plant too much of it. The description of contents don’t really tell you it has everything you need. It is a rich source of available N and like stated is PH neutral.

Right now your plant is looking for P and K to build flower. Your plant shows a modest N deficiency and looks like C as well. (Cal mag or dolomite lime)

I would also suggest a defoliation soon.


Thanks for the feedback and suggestions @Myfriendis410.

Top dressing with manure or organic fertilizer is a slow release solution that takes a little time. I would use something like your average grow micro bloom hydro nutrients at full dose as they work much faster. Just my two cents, good luck!

So I ended up top dressing and defoliating yesterday morning. Had a new taller tent and a fan that can be controlled by humidity so I figured I may as well do that while I was taking it all apart.

pH meter is good quality. PPM is a blue cheapo from amazon.

Just did the run off testing on the one that looked the worst as far as the rust goes and took 2 different samples, the first shortly after it started to run and the 2nd 10 mins later.

pH in is 6.6
PPM in is ~60

pH out is 6.0
PPM out is 600-1200. I could get it to settle for a while around 600 but at times it would jump all over the place and settle in around 1200 also. Crappy meter?

pH out is 6.1
PPM out is 850

Thoughts? This is the first time I’ve ever considered monitoring pH & PPM out.

Always learning!

Unfortunately I’m a soil guy but reading along you Do Not feed any nutes you just to dress ? My understanding of that like posted above that takes Times days to weeks to get to your plant, and if you think you a crappy ph and ppm meter would suggest getting better ones. Your are in flower so I would think your run off should be much higher 1000-1500 range, but soil guy so really not 100% percent. my understanding of pure cocco is that is has no Nutes in it and you are responsible for getting everything your plant need on an almost daily basis cause your soil has nothing it, hope this help, if not just trash it, best of luck happy growing

I use coco coir and peat moss with perlite mix as my soil i mix all nutrients into my soil mix this is the second time using this soil i put live worms in my pots it helps with aeration of the soil plus they put more microbes in the soil my coco coir with peat moss it is more like a proper soil now as much of the coco coir has been broken down by the worms i mix worm castings volcanic rock dust fertilizer and superworm frass and kelp meal and alfalfa meal fish bone meal bat guano and sea bird guano in my soil

I would be happier to see runoff numbers, in soil, to be no lower than 2,000 ppm in late veg. Top-dressing fertilizer is unfortunately slow to work and hard to control. This is why liquid supplements, added during watering, is a good way to get the nutrients to the root zone.

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So my goal was to do these plants organically meaning no chemical fertilizers. The only thing I have around is some miracle grow bloom stuff. If your only options were to feed it the miracle grow, or leave the slow release organics what would you choose?

You can use MG but it crashes the PH of your medium. Organic is tough to do and I see a lot of growers start out organic and end up supplementing with synthetic nutes. The plant doesn’t care where the nutes come from; so long as the quality of materials is high, you’ll be too haha.


I found that out myself burning a few plants in the process but there’s ways around that if you have the intuition

Here are some more photos. It’s just getting worse. At this point I guess I just live with it, let them grow out and learn for next time. It looks a lot like a problem I had last grow but I had assumed it was light burn because I had a smaller tent and couldn’t keep the buds far enough way from the light. For that grow I was using kryptonite soil and just adding water.

I’ve ordered an autopot setup and will do that with straight coco for 2 photo-periods I just started.