Orange/Brown Rust on lower leaves??

Very anxious, this has been an ongoing issue and i'm going to do my best to give all the info needed to help assist in diagnosis.

The lower leaves appear to be developing rusty patches.
Here are some pictures :











- Strain : Ak47 (Serious Seeds) (reg)
- Growing Indoors
- Under approx 200w of CFLS
- Rockwool and hydroton
- DWC Bubblebucket (good quality pump, pumping lots of air) (water is replaced every week and bucket is cleaned with a medical grade chlorine)
- Room temp (highest 27.6c, lowest 21c, avg 23c)
- Humidity (highest 45%, lowest 32%, avg 40%)
- Veg time : 1 month
- PPM's (Currently at 210ppm, my tap water comes out at 90ppm, maybe this is too low but i'm very worried about burning plants)
- Airflow is through high powered computer fans (its not major airflow but its decent, 1 fan blowing air in, 2 blowing out, 1 fan blowing on plant, every morning i also open room up and have fan blowing fresh air in)
- My ph has had a tendency to rise and for a while I wasn't letting it get above 6ph, which made me think this could of caused a calmag lockout? However reading up I came across a few posts mentioning 'Rust Fungus' which i'm very worried about and don't know how to handle if that's the case.
- The roots themselves appear white and without issue. The reason I think its not a calmag deficiency is because isn't calmag supposed to appear on new growth, not lower leaves?
- Bottom leaves are starting to yellow it appears.
- I also had a very minor fungas gnat issue but I have put down yellow sticky traps and haven't seen any since.

- Products used are :
1. Canna Coco A & B (I recognize this is designed for coco but it should work in dwc?)
2. Dutch Masters Root Zone
3. Hydroponic Store PH Down
4. Calmag (Recently bought assuming this is calmag issue, only just started using)

I really hope someone can help, so far asides from the rust it appears to be growing okay from my perspective. I just topped it recently and can see it just starting to bush out. I really hope it can be saved, it's had this issue for about 2 weeks now and is still growing. I'm hoping it's just a simple ph lockout issue because at the start I was a bit anal with trying to keep it at 5.8 and then I realized it's better to let it drift from about 5.7-6.4. Thank you.

Magnesium is a mobile nutrient so deficiency begins on oldest leaves as plant relocates to newer leaves. I think adding the cal/mag is a good idea.

Also you don't mention what PPM scale you refer to that is why it is best to use EC. 210 PPM (on the 50 scale or 70 scale? either way) is low for where you are at with that plant. I would aim for a 1.0-1.2 EC now (500-600 PPM on the 50 scale or 700-840 on the 70 scale) and ramp up from there....plant looks under fed.

It's not the "Rust", that affects the underside of leaves, and will brush off to the touch.

Thank you so much for both reassuring me that my suspicions are correct. You are probably most definitely right about it being underfed, i've just been anxious about burning it but starting tomorrow morning I will begin gradually upping the PPM's because I have been running it quite low.

Tbh I don't actually know how to check my ppm scale, i'm using this kind of generic tds meter


EDIT : Actually screw waiting till tomorrow, upped nutes just now.
Added :
- 12 drops of Canna Coco A
- 12 drops of Canna Coco B
- 1.5ml of calmag
- 1.0ml of rootzone

ppm yesterday was 210 but when I just checked it was 185-190
just raised it to 265.

Ph at 6.1-6.2 (allowing it to rise up a bit so that in can take in calmag)

wish me luck