Can anyone tell me what's wrong?

I am growing under 600 watt mh currently, in foxfarm ocean forest in 7 gallon grow bags, haven't started using nutrients, I have been using plain water until last week I used happy frog fruit and flower to give them some nutrients, and watered again yesterday now the leaves are looking lighter yellow and the bottom leaves are like comepletely yellow and look awful. Looks like it working it's way up, any help would be greatly appreciated, I want to switch to 12/12 soon but want to take care of this problem first.

Anyone out there, could really use some advice thanks..

Looks like nitrogen deficiency. She ate up everything there was in the soil, and is now pulling nitrogen from the older leafs to the fresh growth.

Don't use bloom nutrients until a week or so into flower, not enough nitrogen to sustain vegetative growth. Use grow nutes through veg and a week into flower (until early flower stretch is done) then switch to bloom nutes as the flowers begin to develop.

the lower yellowing I would normally say is a deff

but your fresh growth is pretty light making me think it`s being over fed

carry on with plain water again

then maybe try nute in a week or so but 1/2 the strength you used

I find I feed more than most people I normally do coco and hydro, find myself using 1000ppm+ where most people are using 600 to 800, normally if I get yellowing leaves its due to low N or low K

but yours looks like the extra nutes or some kinda bio stimulants cause the plant to digest its lower leaves

could just mean root growth and its setting up to flower

but to be safe I`d feed less if I was you

Now if you were me you`d go back and feed that bitch more........... but your not me so don`t, lol