DWC Rusting on top leaves - need help!

Fhawila · Tuesday at 6:22 AM

Hi guys ,

I’m running Mills nutrients - plants are particularly big as needed them to stabilise before flipping.
1.7-2 EC
PH 5.8-6
600 uMol Quantum Led
66 F Water temp
73 F Ambient Temp
50% RH
1200 PPM CO2

Some plant leaves are showing these rust spots on them, I supplemented low dose Athena Calmag but hasn’t solved 100% - any thoughts are very welcome!

Mr. Mohaskey · Wednesday at 6:50 PM

Raise your ambient "light on" temp to at least 82f, with co2 I'd say 84-86 would be good. 73f for lights off is good. Lower your EC to about 1.2-1.4 for a little while. RH should be raised to about 60% under the conditions I just specified.

Edit: you using Epsom salts? What nutes are you using?

Mr. Mohaskey · 2025-05-15T07:53:18-0600

Mr. Mohaskey said:
Raise your ambient "light on" temp to at least 82f, with co2 I'd say 84-86 would be good. 73f for lights off is good. Lower your EC to about 1.2-1.4 for a little while. RH should be raised to about 60% under the conditions I just specified.

Edit: you using Epsom salts? What nutes are you using?

Just reread the post and saw Mills nutes. I am not familiar with them so cannot comment on that.

Fhawila · 2025-05-15T07:56:24-0600

Mr. Mohaskey said:
Just reread the post and saw Mills nutes. I am not familiar with them so cannot comment on that.

thanks for your help .
i will raise the day temp (has been on my mind)
EC is currently at 2.2 will lower for a bit but doesn’t look like nutrient burn so much looks like calmag deficiency. i’m trying to grow 5 different strains so that’s not helping…

RH i’m worried about raising to 60% due to mildew mold which i’ve had before (am in costa rica)

Mr. Mohaskey · 2025-05-16T08:36:43-0600

LEDs are an entirely different animal when it comes to ambient temps. Temps need to be higher for the plant to transpire properly, then your humidity needs to be aligned with your stage of growth and temp. Once you get those dialed in your plant will start feeding properly. A lot of growers tend to think calmag issues are the culprit, when the actual factors are more likely Temps, humidity, overfeeding which leads to nutrient imbalances causing issues looking like calmag. Also Epsom salts are great for your plant.

Look VPD charts to help dial in your temp and humidity.

DWC Rusting on top leaves - need help!

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