Help Diagnosing Rust Spots

Hi all, this is my first indoor grow. all has been going really well. thought i had a simple calmag issue, but now i’m not so sure. they started as very tiny, almost perfectly round rust/gold spots on a few leaves but it’s not improving and some of the new growth is now showing. second plant showing a few spots today.

i am not seeing anything raised but looking through a loupe and cheap microscope and it’s not 100% easy to see

I have 2 blue dream photos in the same 2x4 tent
Start week 3 flower
Coco/perlite with Advanced Nutrients Coco Sensi Ph Perfect, feed every other day at 75%, though lately feeding 100% to fix calmag (the base nutes have calmag in them)

I took out the loupe and got some close ups and am now sufficiently freaked out.

the light is bouncing off my countertop and backlighting this leaf. the lighter green ring is not visible to the naked eye.

back of the leaf…

EDIT. well cr@p. i’m seeing the spots starting on the other one now as well.


I’m guessing K deficiency or some sort of lockout by nutrient imbalance. K should be 2 to 1 over P and that’s elemental after the atomic math on K2O.

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Did you have a PH issue within the last 2 or 3 weeks? That can do it. What’s your cal mag dose?

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i use ph perfect nutes which allows uptake at the roots from something like ph 4-8. i’ve tested it a few times in the watering can it’s usually around 5.8-6 but again this isn’t supposed to matter. i use 75% strength and ca is 3% and mg is .9%. usually water 2 gallons each for a total of 20ml base nutes with runoff.

it’s sadly looking less like ca to me. but also the rust spots don’t seem to be raised tho sure does look like rust.

still tempted to flush because what can cause lockout with these nutes is salt buildup.


Well, coco needs to be flushed periodically. Especially at any change in schedule. I haven’t used the AN line but I have heard some complaints about it. If you are using pure R/O likely you are fine.

i am assuming the rust is not loose like mildew.

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It is calcium deficiency IMHO.

I do Hydro and Pro-Mix HP.
Pro-mix is pretty much the same as Coco and easy to go into calcium deficiency. I always add 2.5ml General Hydroponics CaliMagic per gallon. I also use RO so it is a bigger deal. I also always put 1/4 teaspoon per gallon Epsom salt as well in addition to the 2.5ml GH CaliMagic.

I use Jacks for Hydro and GH Flora Trio with Pro-mix.

i tried scraping it and doesn’t seem to want to come off, but the dots are so tiny it’s really hard to see.

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i want it to be Ca. i’ll probably flush and then supplement. they have a calmag bottle that can be added to the base nutes. my understanding is that normally you can’t feed regular calmag together with the base because they turn to glue.

a few older leaves seem to have a few Ca deficiencies but they’re larger, blockier flecks. that’s what’s really raised my suspicion.


You can add to nutes just in the right sequence and not all at once. Silica first always.

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i flushed last night so let’s see if that helps. going to try to keep better track of progression. it’s on every leaf. not sure how fast Ca issues progress but that also may be key to determining if this is mold vs nutes. seems worse today but i don’t have an exact photo to compare.

serenede should get here today.

If you use General Hydroponics, you might find this useful. I have grown quite a few plants on this schedule so it is a proven process. I get at least 5-6 oz per plant in 5 gallon smart pots with 2 HLG XL 320 lights in a 4x4.

It is about 800-920 PPM I believe. The add order is at the bottom. You can feed this every watering with no problems at all if you want.

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thanks will keep this in mind next grow. may just go organic in kind to keep it simple but will see

Just an FYI, i got the Serenade and did a test spray. I’m 3 weeks into flower with all fat white pistils and the spray turned them all shriveled amber.

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these pistils should be all white and shooting straight up. thoughts and prayers that this is a Ca def cuz not sure what else to do. I have some Prestop on the way.

To me it doesn’t look like fungus rust. Rust will usually look like someone painted the leaves solid in the part affected not like paint drops randomly spotted like I’m seeing in your pics.

Good luck

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