Two weeks old; light green leaves, beginning to curl and yellow/rust (pics)

Hello, my autoflowering white russian (moscow) is now 15 days old. When it was about 10 days old the leaves began to get light green.
Now some leaves seem to curl, and get yellow/rusty on the edge of them.

Strain: Auto Flower White Russian
Grow area: DR40 tent (40cmx40cmx120cm)
Lights:400mh with cooltube
Distance from plant: 50cm
Humidity: keept between 40-70 until yesterday, now it is around 45% as the preflowers have shown and I will switch to HPS 400w
tonight when the lights have gone out.
Light schedule: 20/4
Temp: around 24-27 degrees celcius, drops to 19-20 celsius with lights out.

Soil: Gold Label Special Mix
Pot: Air-pot approximately 13 litres from seed.
Watering: Watered completely when first put in soil, have not watered until today again, the pot weight felt light so I decided to water. Ph: 6.0-6.4
Nutrients: No nutrients added on first watering, second watering; added about 0.15-0.2ml/l Gold label Roots and watered pot completely.
Oscillating fan: Have a small fan blowing towards the cooltube and for moving around air.


Help would be much appreciated since its my first grow!

Looks over or under watered and you might need some nitrogen . Hope it works out Happy growing I would check around on plant problems to but I'M sure that what it is. The site has everything you need thigh so looking around might help.

Since I've watered 2 times in 2 weeks I believe it might be under-watering, feels like overwatering is out of the question.
So what do you suggest I do to add nitrogen? I have Gold Label nutrients ULTRA MG, the info on this says:

ULTRA MG
Gold Label Ultra Mg is a nitrogen / magnesium additive for all plant development stages.
It contains high quality magnesium chelate which is easily absorbed by your crop in a wide pH range.
Use continuously on inert mediums and as a replenishment on peat and compost mediums.

NPK=4-0-0+5MG
Guaranteed analysis:
Total Nitrogen N (NO3 4%, NH4 0,1%) 4,1%
Mg (chelated EDDHMA) 5,5%

It also has some magnesium in it, would this be a problem?

Or should I just add Soil A and B which contains other nutrients aswell?

And also, I just watered today, would it be any problem if I watered with the nutrients tomorrow when the lights turn on?

Edit: Btw, can I add the ULTRA MG to a spray bottle and spray it on the leaves instead of watering the soil?

Try adding the soil I would try to get different nutes. I've never heard anything about them or do I know anything about them. I'M a newbie but I've done my research so I will help the Best I can.

Ok so I took one drop of MG ULTRA in 6dl of water and sprayed it under the leaves, and also poured some of it in the soil. Tomorrow I will add little Soil A/B nutrients to the soil and see what happens.

Leaves curling can also be zinc, manganese and iron deficiencies.
Rusty and galvanized nails are good sources.
Just bury them around the stem a half inch down.
Magnesium is a good thing.
It helps unlock the doors to fertilization.
Miracle Gro? All it is is epsom salt (magnesium sulfate) treated with dye and npk and resold at a profit.

Ok so I made a new watermix with gold label roots, soil A and B, I put approximately 1.5/5 of the strength recommended. I then adjusted my pH levels to about 6.2-6.4.
I watered maybe 1.5-2 litres. I also ph-tested the runoff. It showed very low, since my ph level only goes down to 5.8, it was lower than than that. Is this a problem? What should I do?

EDIT: the test on runoff was on a little sample of the runoff, I poured all the runoff in a container and tested it again, it now read about 6.4 So it was not so acidic as I thought. What is the ideal runoff ph level?

Underfeeding and underwatering. Use full str nutes now or things will continue to get worse. Also when plants are healthy dont wait till pot is light to lift ,water when top couple inches dry and saucer is dry. They were nice and healthy until you slowly starved them, still good though.

Okey, but since I just watered a little with 1.5/5 of recommended strength, do you think I should add the rest 3.5/5 of nutes in the water and water again?
How much should I water? Completely or just a couple of dl?

The plants are now doing great again, thnx for the help. Had underwatered and underfed them.