It was probably a good idea pulling them back from the 600w light. How much of the tomato nutes did you use? Full strength? What is the NPK percentage in Tomato grow? Have the leaves started browning on the edges of the leaves too? From the symptoms given, It's most likely nute burn. Next watering, give them just water. If things get worse, you might need to flush the soil. Just keep a close eye on it, and keep us posted. Good luck!