Newby Grow - What is happening? HELP!

Hey guys, I've just got a few pics here of my 5 plants. One of the plants is really small, 2 seem average size and healthy, one (pictured) is tall and is starting to dry a bit, and one is pretty big, (pictured) and has some problems.

They were doing well for the first 2 months or so under one flourescent bulb. Giving them "plant-prod" all purpose 20-20-20 fert. every second watering.

I just put them into 12/12 light (they were on 0/24 before) and have stopped the ferts. They have been in 12/12 for a week now and the plants seems to be hurting. They were planted from seed and are in soil/perlite. Watered with left-out tap water.

Some problems I already know of:

Pots are too small for some...

The grow area is really crowded. I am limited by the amount of room I have and might consider getting rid of some (if they don't all die before...)

There may be slight light leaks during the lights-off stage. Will fix that.

There are a couple plants whose bottom leaves are really starting to dry out and get crispy. Some leaves have lost of burnt, yellow tips. (When I did start fertilizing, i think i did too much.. every watering... cut that down as soon as i noticed yellow tips of leaves).

Please have a look at the pics and tell me what you think!! Any advice is helpful! (sorry i can't figure out how to rotate the pics...)

Thanks

here are a few more pics