This is odd...

[conyaks]

I'm about 3 weeks into growing 3 tomato plants using hydroponics and was curious if anyone has seen this kind of discoloration in a tomato plant.. I'm thinking leaf burn from the light but I'm not sure. I'm just using a 4ft Shop light.. This morning I found one of the tomato plants up into the fixture. thanks

http://img268.imageshack.us/img268/8860/p7230034q.jpg

http://img31.imageshack.us/img31/7084/p7230036.jpg

[mjc]

Looks like a mineral deficiency...possibly iron or magnesium, to me.

[Timmah!]

Depending on what kind of setup you have, I would suggest a few things:
Make sure the roots aren't water logged & thus deprived of oxygen. Make sure the ph isn't too high. Both of these things result in interveinal chlorosis like you have, which is a sign of manganese & iron deficiency.
So: Provide more oxygenation for the roots. When I had a flood table, I had a bubble stone timed to turn on for the duration of the flooding. Adjust the ph if needed. Add some iron & manganese to your nutrient solution. And make sure you don't have salt buildup while you're at it, which can harm the roots too.

[conyaks]

Timmah, I was reading up on leaf chlorosis and found that webgarden has a thread talking about it, but also mentions that no light cycle can lead to leaf chlorosis.. I've been running this shop light since they sprouted, no light change at all. I think if I put them on a cycle they should pull thru?!? The kid at my hydro shop was clueless about chlorosis and told me I shouldn't have to add iron or magnesium as this stuff is provided in my GH nutes that I use...