Septoria?

I would toss it . Reason is . How do you get rid of it ? Putting water on the leafs will make it worse allowing the spores to reproduce more and more ! .
I think its a total loss. You should deep clean your room with bleach as well. Is your tent very moldy and hot ? Interesting how you go them ? They usually are outside gardens .
Now if you were to keep the humidity in check 45 % or less its possible it would stay at bay.
But at this stage ? Why bother . I would start over not risking a plant that could explode into a toxic death .
It is very contagious with other plants .

 

Leaf spots may mean a fungal disease | Gardening in the Panhandle

 

Looks like cal/mag deficiency. Septoria is extremely rare. The rust dots look like calcium deficiency the yellowing between the veins looks like magnesium deficiency.


Just in case

With Daconil® fungicide's three-way protection, you can stop, control, and prevent septoria leaf spot and more than 65 other fungal diseases. Treat tomatoes as soon as weather conditions favor septoria leaf spot, and maintain control with repeat treatments every seven to 10 days.

 

Show the whole plant it looks pale from what I can see meaning lacking nutrients. What nutrients do you use how often how much. How old is the plant and pot size. Have you gotten run off readings? ( ph,ppm )

Take pics in the room light or natural light not under the leds. Some spectrums can give off yellowish colors for plants.. if you can't remove plants from tent just cut your grow light off and use the camera flash

 

How much are you watering until runoff? How much run off. Ocean forest feeds 4 to 6 weeks time varies. Also depends on how much runoff is given. May want to check soil ph. Ocean forest is organically rich and doesn't need to be phed. Only once organic material is depleted and you start using liquid nutrients is phing needed. Your soil ph could be low, or being a month old in a small pot nutrients could be depleted. I would get runoff readings of ph and ppm before continuing any treatment. Slow water not allowing water to stand only water enough to start runoff then only get enough runoff to test. You dont want alot of mixing of old to new and you dont want to water fast making a stream like effect where water is basically running straight through.
If ph is too low doesn't matter how much calmag is given it wont be able to be absorbed by roots

Imo that doesn't not look like leaf septoria,
Last question how many watts and how close?

 

It looks like new foliage is unaffected from whatever deficiency you were facing so I wouldn't worry too much about it. Removing the plant and Isolating with pH'd water was the best thing you could have done. I wouldn't have used the cal/mag. Calcium and Magnesium are absorbed in more acidic mediums; are you checking runoff pH as GrowBuddy mentioned? I would top dress with earthworm castings, aim to lower your pH to 6.0-6.2 and don't feed with cal/ mag. Top dress with 1"-2" of earthworm castings and water thoroughly @ 6.0pH.

I'm assuming you're treating the soil hydroponically? Or did have you amended the soil with compost?