Its hard to tell with so few details and pics it could be:
Overwatering
Overwatering drowns the plant by stopping the roots getting much needed oxygen. Make sure the plant pot feels alot lighter let the top soil dry a little then water. Look into hydrogen peroxide.
Soil
I have found that useing shit soil kills plants. The soil your using has time release nutrients which means it burns roots that could be the yellowing. The plant is trying to tell you its deficient of nutrients because the time release nutrients block uptake of the real nutes your trying to feed the plants. Buy bio bizz plagron ect please I had to bin 5 plants my first go by making this mistake.
Nutrients
Always use half the recomended fertilizer full strength is almost always to strong especialy considering your using only 200w envirolite. thats about all I can give considering I don't know strain and minor details I hope you do well PM me with all details if this doesn't work thanks.