Rust Spots - Mid-Flower

Hey all - started getting some brownish rust spots a few days ago…and they seem to be popping up with more frequency daily. Any ideas? Leaves seem to be curling up a touch now as well. Maybe a magnesium deficiency? Epsom salt foliar spray ok in mid flower? Pics below (didn’t do a great job focusing, sorry).

Grow details:

Medium/grow method: FFOF/Perlite; 3 gallon fabric pots.

Feed: 1/2 dose of Fox Farm Trio (just cut out the Grow Big last feed); full serving of CalMag every other feed (was doing 1/2 serving, but just upped it for feed last night thinking that might be my rust issue); 1/2 serving of Silica every other feed; 1/2 serving of Fox Farm Beastie Bloomz for last 2 feeds; full serving of Mammoth P. Last feed was 760 PPM, pH 6.3; runoff was 840 PPM, pH 6.3. Feed, water, feed, water (every other other day). Runoff to about 15%. I flushed with pH’d water 2 weeks ago – just to reset the medium a bit (per FF soil schedule).

water source: city water; runs a little acidic, so usually have to PH down to about 6.3-6.5.

Strain/age: Blueberry Auto ILGM. Week 9. Been flowering for about a month I guess.

Light: HLG 260xl - about 18 inches at 160 Watts; 20/4 light schedule

Climate: Indoor Tent; running a Cloudline T6 inline exhaust fan with Carbon Filter; passive intake; couple desk fans pushing air around; Temps: 75 during the day; 65 at night; RH: 38-48.

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Looks exactly what i’m going through right now.

Think it’s a calcium deficiency. I think mine is caused from Nute lockout.

I just did a flush, yesterday, and will be monitoring it moving forward.

Good luck


Thanks, let me know how your flush works out if you don’t mind! I’m hesitant to flush again because I just did it two weeks ago, but might need to i guess. Good luck to you!

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Are you checking you run off PH & PPM?

Mine were not adding up to in vs out. I had just flushed a couple weeks prior too, but apparently one plant didn’t flush all the way.

Yeah, my last feed (last night), I fed 760 PPMs with pH at 6.3; runoff was 840 with pH at 6.3. So I feel like I’m in pretty good shape there. Or is it always bad news if the runoff PPMs are higher than the feed?

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I have always thought a higher PPM runoff is not a good sign. It means there is a buildup of nutes in the soil.

When I see that with my plants I do one more watering on schedule and if still higher I flush. I’m just verifying it wasn’t a fluke

I don’t recall in two years ever having ppm equal to or less than the feed ppm. I checked my last grow records, ppm 830 runoff 1200 was the lost. Most 1500 - 2200. I did flush one plant once. PPM jump to over 4000 and PH dropped .2. Used Flawless Finish. It was back of track for the rest of the grow. The plant showed absolutely no signs of any problems. I flushed as a precaution and because both ph & ppm changed more than they should.
My soil ppm are always all over the place so I tend to pay more attention to the ph side of runoff. If it drops more than .25 from average feed ph, it gets my attention.

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@beardless You may be right. I have always had a lower PPM on out than going in.

When my ppm has been higher in the runoff I start to see nutrient deficiencies on my plants.

@Covertgrower @jetlag @Nicky @Hellraiser @Not2SureYet @AfgVet @Caligurl @MeEasy @JaneQP - can one of y’all shed some light on this?


I always target 100 - 200 over for the run off. Less than what is going in tells me I am not feeding enough :grin:


If your runoff PPM’s are lower than the input it means she is still hungry. Runoff numbers a little higher should be no issue. If I am feeding 800 and runoff comes out at 1000 I don’t stress about it. Just monitor your runoff as @beardless indicated. If it starts creeping up and PH is ok, then I start thinking of flushing, and then only if i start seeing changes in the plant.


Since my pH/runoff appears to be in pretty good shape, any thoughts on what my issue might be in those pics above?

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Any thoughts on what my issue might be in those pics above?

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how about pictures of the whole plant. Is this happening all over the plant?


I suck for diagnosing things. If that was my plant. I would be looking at my ph first off. Once it gets off. it starts blocking other things out. I am not telling you to do this. just what I do. If I was to see that one just a few leaves. I would remove those leaves. That way. It would be easier to see if I was fixing an issue or not. I can look at the same leaves and my brain would tell me half were not like that before. I am in coco. but I do much better with a lower ph than on the higher side. I used to be able to drag @Myfriendis410 over to look at my plants and let me know what he though. He is a lot sharper than I am. :slightly_smiling_face:


@emgoldslo. My one butt head plant named Gary always has problems. For some reason her soil pH was above 7. I flushed and added cal mag. She is ornery and I have to give her a big flush a week and then feed her later.

Everyone needs a Gary.


Here are a few more pics. My lights actually just came on at 3:30 EST, and the issue had definitely spread since the lights went down four hours ago. The effected leaves are also very crispy/crunchy to the touch…I gave a little pull on one leaf and it just cracked right in half. The sides of the leaves are really starting to curl upwards as well. This issue is really coming on fast. Is it possible that it’s a fungus or something? It doesn’t rub off at all, so I doubt that’s it. Ugh…any ideas? Thanks in advance!!

Thanks for taking a look! It’s not every leaf at this point…but there are leaves on all parts of the canopy that are showing this issue. That said, the leaves that aren’t getting direct light on the inside of the canopy appear to be unaffected…or at least less affected than the ones that are in direct light.

In my dreams. Never even close to those numbers even the last week before harvest when they are on water only. Are you soil? My soil is heavily amended so I figure it is what it is.

Are you following the FF feed schedule and if so what is the TDS of your nutrient solution going in? Have you ever done a flush?

FF recommends flushing at regular intervals to avoid salt buildup in the media. Looks like calcium def but could be caused by a lockout.

COPY/PASTE the below list into your forum post.

Answer these simple questions the best you can.
If you do not know, or do not use something; Just say so; Or post
NA (non applicable)

  • What strain, Seed bank, or bag seed
  • Method: Soil w/salt, Organic soil, Hydroponics, Aquaponics, KNF
  • Vessels: Pots, Grow beds, Buckets, Troths
  • PH of Water, Solution, runoff (if Applicable)
  • PPM/TDS or EC of nutrient solution if applicable
  • Indoor or Outdoor
  • Light system
  • Temps; Day, Night
  • Humidity; Day, Night
  • Ventilation system; Yes, No, Size
  • AC, Humidifier, De-humidifier,
  • Co2; Yes, No

Always try to upload a clear picture of any issues you may have to allow the community to assist you.

Add anything else you feel would help us give you a most informed answer should be included. Feel free to elaborate, but short and to the point questions and facts will help us help you in a more efficient manner :slight_smile:


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Hey thanks for chiming in!

  • What strain: ILGM BBY Auto
  • Method: FFOF with 30% perlite
  • Vessels: 3 gallon smart pot
  • PH of Water, Solution, runoff (if Applicable): 6.3 in; 6.3 out
  • PPM/TDS or EC of nutrient solution if applicable: 760 in; 840 out
  • Indoor or Outdoor
  • Light system: Indoor
  • Temps; Day, Night: 75/65
  • Humidity; Day, Night: 45
  • Ventilation system; Yes, No, Size: Yes, 6 inch cloudline
  • AC, Humidifier, De-humidifier: No (but was running humidifier earlier in grow)
  • Co2; Yes, No: No

My last feed (last night) was 760 ppm going in, and 840 ppm coming out; and pH was 6.3 going in and 6.3 going out. I had been giving a 1/2 dose of CalMag every other week, but when this issue popped up I thought it might have been a calcium or magnesium deficiency, so the feed last night included a full serving of CalMag. I’m not sure how long it takes for the nutrients to work their way through the plant, but the problem is definitely worse today than it was before I fed yesterday. Thanks!!

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