5 weeks in flowering, first time with RO water

What up RIU!?

I’m 5 weeks into flowering in a new micro cab I built and having some typical brown spots on the lower leaves working their way up the plant which tells me I’m seeing a cal/mag deficiency. I’m using RO water this time around, for the first time ever because I’m in a new city with horrible tap water.

The thing is, I ALWAYS have this happen around this time. I’m not sure if it’s normal as the plant starts nearing the finish line and is just using up its resources and I should just let it ride or if it’s something I need to correct. I’ve grown quite a bit, this is far from my first rodeo ... but this has been a pretty consistent occurrence with all my grows, whether I’m using Tap water or not.

Anyway here’s the deets of this grow.

Microcab armoire inside dimensions 23” L x 16” D x 35” H.
Solsheet X2 w/ 120 watt driver running at approx 25,000 lumens
4” AC infinity fan/scrubber combo 205 cfm
Approx 2.5 gal soil container
Organic soil fox farms happy from with added perilite and worm castings and a granular fert(tomato tone) with dolomite lime

.... and I’ve been hitting her pretty heavy with Neptune’s fish/seaweed the last week










Here she is at five weeks:










And here are the leaf issues I’m seeing. You can see the brown spots that I believe are a cal/mag issue but she’s also starting to fade too, which is a bit early for my liking.











Sooo ... what do you think? Is it something I should try to correct? My next grow will be a 12 week Sativa, so I can’t have them starting to fade and showing deficiencies at 5 weeks.

OZZZ said:

What up RIU!?

I’m 5 weeks into flowering in a new micro cab I built and having some typical brown spots on the lower leaves working their way up the plant which tells me I’m seeing a cal/mag deficiency. I’m using RO water this time around, for the first time ever because I’m in a new city with horrible tap water.

The thing is, I ALWAYS have this happen around this time. I’m not sure if it’s normal as the plant starts nearing the finish line and is just using up its resources and I should just let it ride or if it’s something I need to correct. I’ve grown quite a bit, this is far from my first rodeo ... but this has been a pretty consistent occurrence with all my grows, whether I’m using Tap water or not.

Anyway here’s the deets of this grow.

Microcab armoire inside dimensions 23” L x 16” D x 35” H.
Solsheet X2 w/ 120 watt driver running at approx 25,000 lumens
4” AC infinity fan/scrubber combo 205 cfm
Approx 2.5 gal soil container
Organic soil fox farms happy from with added perilite and worm castings and a granular fert(tomato tone) with dolomite lime

.... and I’ve been hitting her pretty heavy with Neptune’s fish/seaweed the last week

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Here she is at five weeks:


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And here are the leaf issues I’m seeing. You can see the brown spots that I believe are a cal/mag issue but she’s also starting to fade too, which is a bit early for my liking.



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Sooo ... what do you think? Is it something I should try to correct? My next grow will be a 12 week Sativa, so I can’t have them starting to fade and showing deficiencies at 5 weeks.

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This is the time frame for magnesium and calcium deficiencies to show. Even using tap water. When I switch to 12/12 I feed a couple of veg feeds because they’ll need it. I also add 1/2 tablespoon cal mag to the feeds or water through about week 4. I don’t keep chasing it with cal mag after that but you are using RO water. Your call but I would dose a teaspoon per gallon and benefit from the nitrogen in it.

How high are the lights?

Nice setup. Nice job on the plant.

Great setup and beautiful training! I'm in coco coir with RO water so I use cal-mag throughout the grow, although I'm cutting back now in late flower. I think hotrodharley is spot on recommending Cal-mag at 1 teaspoon per gallon. Is your ph in range to uptake all the nutrients?

hotrodharley said:

This is the time frame for magnesium and calcium deficiencies to show. Even using tap water. When I switch to 12/12 I feed a couple of veg feeds because they’ll need it. I also add 1/2 tablespoon cal mag to the feeds or water through about week 4. I don’t keep chasing it with cal mag after that but you are using RO water. Your call but I would dose a teaspoon per gallon and benefit from the nitrogen in it.

How high are the lights?

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Hotrodharley, thanks for stopping by. That’s what I’m thinking, that I need to add some cal mag, also I think I’m going to add some kelp to the initial mix and also add a top dressing of kelp When I flip to flower to try to up the micro nutrients. Lights are way above the tops, probably 12” or so, but I’ve seen growlogs with people getting within inches of these solstrips with no issues so I don’t think that should be causing any issues? I purposely flowered this girl out small and early because I have some Panamas on deck. This was simply a freebie test grow. I always do a freebie test grow in a new environment to make sure all the kinks are worked out before breaking into my good genetics. Strain is a chocolate mint OG (OG x GDP) by Humboldt

SheeshM said:

Great setup and beautiful training! I'm in coco coir with RO water so I use cal-mag throughout the grow, although I'm cutting back now in late flower. I think hotrodharley is spot on recommending Cal-mag at 1 teaspoon per gallon. Is your ph in range to uptake all the nutrients?

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Hey there Sheesh... thanks for the input. I’m not sure of my PH, I don’t have a PH pen but this is organic soil so it shouldn’t be necessary. As mentioned my mix is happy frog soil, with added perilite and worm castings with a granular fert and dolomite lime at 1 cup/cu ft of soil as recommended. The dolomite lime should be buffering the PH. Although maybe I should have top dressed with a bit more before starting Flowering, probably wouldn’t have hurt.

I think from here on out I’ll add cal mag at one teaspoon per gallon to my RO water, and add a top dressing of kelp when I flip to flower. That should straighten things out I believe.

My usual soil mix is promix, but I couldn’t find it locally so I used happy frog as the base. I have since gotten a bag of promix shipped in so I mixed it 50/50 with the happy frog/castings/perilite mix as it was a little heavier than I like. I always mix in the granular fert in the container itself so my stored soil is just a base mix and I can add the ferts as I see fit whether it’s for a seedling, veg, or flowering container. Either way, regardless like I said this seems to always happen around this time on all of my grows, so I need to get it sorted out before taking on these longer flowering sativas. Next up is ACE Seeds Panama. I have six in my veg cab now. I’ll go extremely light on the nutes with that one, but probably still do small top dressings of kelp when I flip to flower and on weeks 4 and 8. With cal mag at 1 teaspoon per gallon throughout the grow until the end when I’m ready to let her start fading.

Veg cab:

23”L x 16” D x 19” H

3000 lumens mix spectrum under cabinet LED strips 5000k/6500k

Homemade carbon scrubber (mesh pencil holders) with a noctura 120mm industrial fan 109cfm and noctura pc fan controller.

Another question regarding cal mag and RO water. So I understand that RO water doesn’t have any buffering capacity, does adding cal mag to RO water add this missing buffering capacity? Im assuming yes, since it’s adding minerals to the water?

OZZZ said:

Hotrodharley, thanks for stopping by. That’s what I’m thinking, that I need to add some cal mag, also I think I’m going to add some kelp to the initial mix and also add a top dressing of kelp When I flip to flower to try to up the micro nutrients. Lights are way above the tops, probably 12” or so, but I’ve seen growlogs with people getting within inches of these solstrips with no issues so I don’t think that should be causing any issues? I purposely flowered this girl out small and early because I have some Panamas on deck. This was simply a freebie test grow. I always do a freebie test grow in a new environment to make sure all the kinks are worked out before breaking into my good genetics. Strain is a chocolate mint OG (OG x GDP) by Humboldt



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Your lights are too close in my opinion.

hotrodharley said:

Your lights are too close in my opinion.

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That is the veg cabinet, those plants are in veg doing well (those are very low powered under the cabinet LEDs)

Here is the flower cabinet.... I’m 13” away from the solstrips with a 78 deg ambient temp:






And as mentioned, this happens in every grow I’ve ever done. In 4x4 tents, 3x3 tents, with hps lights and HLG 550 QB boards.... it’s defintely not a lighting/heat stress issue... as it starts at the BOTTOM of the plant and works it’s way up. I think the cal mag will probably solve the issue. I’ve ordered that and some kelp meal and will try it on the next run.

Had exactly the same problem when I switched over to organic soil and clean water. Check out Cal-mag plus by general organics; it is safe for organic living soil grows whereas most soluble liquid cal/mag is not. Alternatively you could try to hydrate some d-lime or epsom salt by bubbling in water but it must be dissolved to go to work fast.
You can eventually get off of using a liquid cal mag altogether adding dry mineral forms to your mix when recycled. Garden gypsum, epsom salt, d- lime, crushed oyster shell, and composted eggshell are good sources but it takes awhile for these to break down completely and become available in the soil. I have been off the bottled cal mag for over a year now but it took a couple years of recycling my soil over & over to get here.

Those cabinets are great.
If you're worried about staying organic, you might want to look up eggshell tea. Adds calcium and a few other micros. You can also mix the used eggshells into your soil, the slight acidity will leach the calcium out over time.
Just out of curiosity what was wrong with the tap water?

Richard Drysift said:

Had exactly the same problem when I switched over to organic soil and clean water. Check out Cal-mag plus by general organics; it is safe for organic living soil grows whereas most soluble liquid cal/mag is not. Alternatively you could try to hydrate some d-lime or epsom salt by bubbling in water but it must be dissolved to go to work fast.
You can eventually get off of using a liquid cal mag altogether adding dry mineral forms to your mix when recycled. Garden gypsum, epsom salt, d- lime, crushed oyster shell, and composted eggshell are good sources but it takes awhile for these to break down completely and become available in the soil. I have been off the bottled cal mag for over a year now but it took a couple years of recycling my soil over & over to get here.

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Thanks for the info... wish I would have seen this sooner I just picked up a bottle of botanicare cal mag.... sounds like this will kill off my beneficials then?

OZZZ said:

Thanks for the info... wish I would have seen this sooner I just picked up a bottle of botanicare cal mag.... sounds like this will kill off my beneficials then?

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Can anyone point me to some research about exactly how synthetic nutrients are supposed to kill beneficial microbes?

CanadianJim said:

Those cabinets are great.
If you're worried about staying organic, you might want to look up eggshell tea. Adds calcium and a few other micros. You can also mix the used eggshells into your soil, the slight acidity will leach the calcium out over time.
Just out of curiosity what was wrong with the tap water?

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Thanks Jim.... it’s chicago water.... and while I don’t have a Ppm meter or a ph pen I can tell you this, the sh*t is nuclear lol. Smells like a swimming pool coming out of the faucet and even letting it sit for 24 hours the plants were not doing well when I used it from the tap.

Besides that.... I WOULD like to recycle my organic soil, and salt buildup from the water source over time is an issue. So that’s the reason I went RO. Plus I needed one for our drinking water, I use the waste water for our laundery... it goes right into the washing machine and then we run a load so there’s no waste to speak of. I think I’ll start adding crushed egg shells to my worm bin .... try to get it introduced to the soil that way. Maybe I’ll grind them up in an old coffee grinder first.

So at this point my soil is a fresh mix of FF happy frog with added perilite and worm castings with dolomite lime..... but I noticed it was a bit to heavy for me and didn’t drain as well as I’d like (I was a little heavy with the castings) so I cut that mix 50/50 with straight promix and added an appropriate amount of dolomite lime to that. I keep that in storage as a base mix then add my granular fert (right now just using dr earth 4-6-3) directly to the pot a week or two before planting and keep it most. I know I should mix the amendments in and let it cook but the problem with that is I want to run some light feeding sativas that don’t need anything other than the light guano that is in the happy frog and the extra castings. If I mix the ferts/amendments in straight away I fear the base mix will be to hot for them, not to mention seedlings or cuttings.

Anyway, I’m gearing up to implement blumats and I do want to recycle my soil, so I want to use RO to avoid salt buildup in the soil. I had issues in the past trying to recycle soil that was drip fed with tap water... and I’m certain it was due to mineral buildup in the soil. Maybe the answer is working on my soil mix to compensate for the straight RO water.

OZZZ said:

Thanks for the info... wish I would have seen this sooner I just picked up a bottle of botanicare cal mag.... sounds like this will kill off my beneficials then?

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No idea; general organics cal mag plus is OMRI rated. That I know for sure is safe for living soil. Once you get some minerals broken down into your mix for awhile you won't need to give soluble cal-mag.

CanadianJim said:

Can anyone point me to some research about exactly how synthetic nutrients are supposed to kill beneficial microbes?

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Salt based chelates dry out the bodies of microbes. High npk values can upset the fungi that absorb nutrients. Adding some synthetic nutes does not spell instantaneous death; you can add compost to replenish their population. You can give your plants nutrients in living soil but then it's just more difficult to keep your grow water only.....

"Chemical fertilizers, pesticides, insecticides, and fungicides affect the soil food web, toxic to some members, warding off others, and changing the environment. Important fungal and bacterial relationships don’t form when a plant can get free nutrients. When chemically fed, plants bypass the microbial-assisted method of obtaining nutrients, and microbial populations adjust accordingly. Trouble is, you have to keep adding chemical fertilizers and using “-icides,” because the right mix and diversity—the very foundation of the soil food web—has been altered."

-Teaming With Microbes by Jeff Lowenfels

Week 6 12/12 ... looking frosty

Sample bud last night at only six weeks to test for potency was surprisingly potent but short lived... which makes sense as I’m only 6 weeks in. Have to take her down in 11 days though as we are leaving for vacation and I need time to get her stabilized in jars for the cure.