Feeding once a week is actually the standard for me. It's worked great for me in the past for outdoors, but I wouldn't know about indoors. I was wondering what the N-P-K is on the tomato feed you give them?

It doesn't look like serious burn, but it's getting there. Flush like NativeOrganicFarmer has suggested and see how the plants react to that. Do you have a pH meter?

The best nutrients that I've been using are organic, whether you go General Hydroponic's Organic line, or Advanced Nutrients' Iguana Juice.