So you are at 1400. You are going by the directions on the bottle? They look healthy as all hell. I would suggest just topping them off with water for a week then bring them back up to 1800 (1400 after subtracting for hard water) then top with water for another week.
Either that or start using the Lucas Formula.
http://www.cannabis-world.org/cw/showthread.php?t=892
What brand of ferts do you use? I have a friend who doesnt even own a PPM meter and he measures according to the directions on the bottle, tops off with water, and changes out his solution once a week.
Of course with a 55 gallon drum you would most likely want to change them out once every three weeks or so.