I agree coco should never dry out and ideally stay 90-100% saturated.

The pots are a good size so yes you can get away with less often and runoff seems good but you shouldn't need a gal and a bit to get runoff. That suggests watering frequency is to low

Using about 1/4 gal of water should get you 10-20% run off that means 750ml-1L of feed. If doing 1L you should get 100-200ml of runoff. If you are getting less you need to feed more often. If you are getting more you can feed less often. 600ppm would probably serve you well at this point.

Raise the light adjust the feeding and things should smooth eight out after probably a week.