I would just flush them to be safe, it cant hurt. Then start slow with the nutes and let the plants build up a tollerance to the amount before incresing from say a 1/4 then a 1/3 then 1/2, i wouldnt go past a 1/2 tho, 1/2 strenght always worked for me, i use Fox Farms Tiger bloom in flowering and thats all i use. first 30 days of vegging i use nothing but FFOF soil and plain water ph'ed at 6.8, then right to the Tiger Bloom 1/4, 1/3 then 1/2, when they go into flowering 12/12, maybe a Full dose for the last feeding before the final flush before harvest (at the 6 or 7th week)