Rusting on leaves - CalMag/Phosphorus deficiency or Mold?

Hey guys,

First time grower. Have gone through the over watering process, let the plants dry out completely flushed them w R/O. Then gave them some light nutrients. All Vegamatrix nutrients - organic soil with perlite/vermiculite at bottom of pots. I believe I made the mistake of not mixing the perlite into the organic soil bc I feel as though the roots aren’t getting enough oxygen. I’m also supplementing with CO2 when I’m able to get a tank. I have no idea what the rust is or where it’s coming from. It doesn’t appear to be mold but the leaves are just slowly dying randomly so it may be. Idk. Help! Also, let me know what more info you need. I’m using 22Qt Pots with a VIVASPECTRA 1200W LED.


Hi. Welcome to the forum. First those girls look lovely with the exception of those tips u just posted. Think possibly you went too high on the feed. Just my first thought. Looks like tip burn… how far away are those lights? And you said you recently feed. Is it possible u could have went overboard?


Do you know what your PPM and Ph is? That would help.


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 = NA

  • Strain; Type, Bag seed, or NA
  • Soil in pots, Hydroponic, or Coco?
  • System type?
  • PH of runoff or solution in reservoir?
  • What is strength of nutrient mix? EC, or TDS
  • Indoor or Outdoor
  • Light system, size?
  • Temps; Day, Night
  • Humidity; Day, Night
  • Ventilation system; Yes, No, Size
  • AC, Humidifier, De-humidifier,
  • Co2; Yes, No

If you can, upload a picture of your plant. It helps the diagnosis, if needed.

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


Answer these questions as best as you can so we can help diagnose the issue
Did you ph your Ro water
I know my Ro water is in the 5.3 range so i need ro ph up mine
My first reaction to the pictures was aslo light burning as well @PurpNGold74

Good to know. Im on a winning streak today :joy::rofl::joy:

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Ok here’s some updated info:

  • Strain; Strawberry cough

  • Soil in pots w a Soil pH approx 7.5.

  • System type - Vermivulate/Perlite mix at bottom of organic soil mix.

  • What is strength of nutrient mix? N/A - will be soon.

R/O Water often has difficulty determining pH if it’s truly 000ppm until something is added to it I’ve found. Otherwise my meter (which has been calibrated) indicates pH as anywhere from 3.8 to 8.3, though generally more acidic.

  • Indoor 5x5x8 Tent

  • Light system, 1200W (600 True Watts) VIVASPECTRA LED w/ Bloom and Veg Switch’s

  • Temps; 65-80F

  • Humidity; 44 Day, 64 Night

  • Ventilation system; Yes, AC Infinity CLOUDLINE T6, Quiet 6” Inline Duct Fan with Thermostat Speed Control -

  • AC, Humidifier, De-humidifier, - All three.

  • Co2; Yes, - @ approx 1000-2500ppm.

Also, is CalMag something I can (or should) apply foliarly? My plants have seemed to have dried out at this point and I’m showing a soil pH of 7.5. I’m just going to wait until they tell

me they need water before watering them again.

However, when I do: What would you guys recommend?

R/O pH adjusted water or just plain old tap water with a reasonable TDS?

Or a very light nutrient solution added?

I use Vegamatrix Amp-it/Boost/Grow/Bloom/Big n Sticky (in varying degrees depending on plant stage development) and Great White Mycorrhizae. I’m planning on letting them recover for a bit and then putting them right into flower. Please - let me know what the ‘collective’ recommends.

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I pruned a lot of the dead foliage as you can see. Tried not to take more than 20% per plant and left as many fan leaves as possible.

What kind of soil?

How and when are you testing ph? You’re correct ro water won’t test well. But it should test fairly easily after nutes are added. What concentration were you mixing nutes at? And what frequency are you feeding?

Do you have any pics of when this first started? At quick glance your original pics look like nute burn that got out of control. In which case adding a bunch of calmag will probably hurt more than help. And you stripped all the leaves, so I’d hate to shoot from the hip too much.

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You should have no issues with using straight R/O water and don’t worry about PH’ing it as it will immediately be driven to the soil PH. You will indeed need a dose of cal mag but I would wait until your next watering. Add cal mag then PH your solution to whatever medium you are using: soil is 6.3 to 6.8. I would suggest staying on the low side of that.

It’s not mold. I would guess the soil is responsible for burning the plants. Can you tell us exactly what the soil is? A picture of the contents would be helpful.

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Ok here’s some updated info:

Update: Fed them today and applied Foliar spray of CalMag under dim light as not to burn the leaves.

TDS 409
Ph 5.65
5ml/Gal CalMag
5ml/Gal Grow 5-2-3
Fed 1 Gal - .25 gal per plant.

22 Qt pots w organic soil from a local farm that tends to compress; so I’m not trying to over water - usually I use .5 Gal per pot. If they respond well I will try more volume a little at a time as they absorb the water/nut’s. Hoping the CalMag works :confused:

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