Plant is turning yellow

It's getting worse

I used formulex at 1/4 strength

Gave a good water with run off

But it's not solved the problem

All the other plants are looking good

The other plants are smaller but look thicker

This plant is taller but skinnier

Temp - 84F Max, normally 80ish
Soil- bio mix all mix
Water - soon as it's an inch dry, normally every other day or every third day
Light - 600w HPS
Pot - 15 litre
Strain - Super cheese
Nutrients - formulex 5ml per 1litre water

I treat all the plants the same but this one is dying on me.

HELP!!!!!!

Sometimes you literally get a bad seed...

With that said, why is this little thing flowering?

It's auto flower super cheese

Apparently these start to have small buds from 4 weeks+

Flush, and check ph. Then don't give nutes unless you see a deficiency.