Flush with your current feed and top water for a bit. Using autopots this grow myself. 2.5 weeks in flower after 5 week veg from seed. I'm feeding slightly less than you. Can't wait to tie them down abit this weekend.
2....600's pushing it on a 15A. MAX load. 12 amps is about max for a 15 amp breaker. Shit gets hot...especially wire in its upper range. A loose or bad connection anywhere and bad things happen fast...especially on electrical circuits being pushed.