It sounds like you might not be getting enough light. Make sure the plants have enough room so they don't block out light for the smaller plants. Try putting the light closer to the plants but be careful not to to overheat or burn your plants.

The light is right over them. The tomato plant I have in the system has grown past the light. Soon I'll be moving it to a different spot, but its not really covering the others. Most of the plants are exposed to the light with no interference from other plants blocking them and they are still leaning over. What other things can possibly cause weak stems?

Thank you for responding.

If they're long and skinny, that is normally lack of light. Not sure what kind of light you're using but if it is flourescent, they need to be within about 2" from the top of the plant.
Have you considered taking them outside?
Another possible problem is they're too wet. is your medium submerged in the nutrient?
Could you post some pictures?
How do the roots look? what color are they?

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In Golf Course Management Calcium Nitrate is used to make Greens run faster. Calcium Nitrate cause strong stem strength in Both Hybrid Bermuda and Bent Grass.

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I am using a high pressure sodium light. Its a 1000, but I have it set at 400 for now. There's a pic of almost all of the plants. Its a bit messy looking, but you get the idea. I took some close ups, but it seems I can only post 1 pic at a time. The medium is not submerged. They really haven't grown a root system yet since I put them in the system. The tomato plant looks like its blocking the light to the other plants in the pic, but its not. There is enough light reaching all of the little guys.

Hope to get this solved so I can be a happy grower!
Again thanks for all the help, guys :)

Lack of air movement will cause weak stems. Also, pythium, aka root rot, is also known as "falling over disease" or "damping off." If the stem appears pinched and the plant can easily be pulled in two, then it's damping off.

From what I've read, (I grow outside and have only researched using lights) HPS lights tend to put off light high in the red spectrum but low in the blue spectrum. Vegetative growth requires an abundance of light in the blue spectrum for proper vegetative growth. I'm going to guess the plants are leggy because of the wrong kind of light with a bit of being so far from the light. Even the tomatoes, though they appear to be growing fine, are not as dense as they could be. they have a very large internodal spacing.

I'll have to add a light thats more in the blue spectrum and see what happens. Which light would any of you suggest that would be the best to try with?

Thanks you for all the help!

Chances are that your ballast is switchable between HPS and MH. The metal halide bulbs are the ones you want if you want blue spectrum light.

Some plants are picky about the light spectrum and some are not. The pepper plants I grew over the winter couldn't care less which light bulb I used. If you go over to the 420 forums, you can see that their plants are very susceptible to the light spectrum and they only use the HPS lights to flower, not grow. I have no idea if the tomatoes and herbs you are growing will respond better to a blue light or not.

Tomorrow I plan to go to a hydroponics store to pick up a MH light. Hopefully it will work. I have a digital ballast, not sure if it is switchable. I'll ask the guy at the store if it is. If its only a light issue that would be awesome! Thank you all for the help! I'll update when I get the new light and had it for a few days to see what happens to let you know if it worked or not.

Again Thank You!