help what is wrong with my plants

they have been growing for almost 2 months, i use a 23watt light with 5000k, for the soil i use organic vigaro, water i use distilled water and i water them when the top soil is starting to look dry, not super dry, but damp. they are on a 18/6 hr light cycle.

the leaves started to look yellowish about a week ago, but the top of the plant seems to be growing fine on plant b but plant a is growing but its not growing out.
bare with me im a noob.

over watering water when soil is dry

You've been growing that for two months??? That's crazy you haven't given up yet, usually I'd get a plant to be around 1 1/2 - 2 ft by then.

This does look like over watering, make sure you have a drainage system, as of now I'd let the light on them for 24/7 til they dry, then water them once every 3-5 days, just make sure it's dry first, you should probably also transplant right now as you may have mold forming.

Make up a third pot with just dry soil. Use that as a weight reference. It'll tell you when to water.

And add some more lighting!! cn