Help with wilma system?

Hi people,I have 2x 8 pot wilma systems and my plants are 3 weeks 12/12 has anyone had exp or knows if i really need a nute change,the tanks are 80L and im adding at least 15L of fresh nute a day 105L a week ec is pretty stable 1.8-2.1 ph 5.8,dont want to throw nutes away if not needed some say totally change every 2 weeks? any advice would be cool thanks.(2xplants per 11L pot,special kush,lemon skunk,chiesel,green bud and whitewxBB)

i personally have not, but they are expensive. try www.vertigrowsystems.com. they are very similar and much less expensive and more versatile.