Help, I Think my Plant is Sick!!!! Pics Included

Hey RIU, my plants are about 3.5 weeks old, they are in FoxFarm Ocean Forest Soil 20/4 light cycle... When i went to check my plants today i noticed that one of the leaves are curled down and that the leaves are two different color green, a dark green (most of the leaf) and a light green around the tips. I just fed the plants 1/4 strenght of Big Bloom and Grow Big (first feed) and i also switched my lights form 4 23w CFLs to a 400w HPS system... Rep with Help. Thanks in advance RickRolled

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...anyone?...

Possibly too much Nitrogen?

How would i go upon fixing this issue?

Flush the soil and stop the nutes for a week.

Chances are you are watering it too much or adding too much nutrients to the soil already.

Fox Farms Ocean Forrest has all the nutes that young plant will need for a week or two longer. Here is a list of ingredients I cut and pasted.

Fox Farm's Ocean Forest is a unique potting soil that combines the best fertilizers found on land with the finest sea ingredients available. The result is a rich, light, organic potting soil that encourages healthy root growth, disease resistance and leafy foliage. Ocean Forest consists of rich composted forest humus, Spaghnum peat, bat guano, fish, crab, shrimp and Norwegian kelp meals, premium earthworm castings and oyster shells to ensure a balanced pH.