They look good to me definitely not dark green.Sounds like your babys are hungry and could use a lil more nutes. Are they lighter green or darker?
Up it gradually till you see little to no change in ppm's day to day
(id add water + nutes)
I do it all the time.. the rule of thumb is dump your res after youve added back the original full amount of water.i read
that its not good to add nutes on top of old nutes
because it may cause lockout..