looking Stella my friend, top job
... is that the blue cheese up front ? if so looks like you got a good flush on it
... tricky running a rez for 4 different strains at different ages and finding that balance that keep them all happy. That's a real challenge that. You could be getting a big swing in who's the hungriest.. also have to take into account that some plants do yellow out by them selves later in flower even if your still feeding.
just off the top of me head... you could run 2 rez's, one for veg / start of flower and one for later in flower. You can keep that perpetual grow going then, just got swap the plants over to the required rez when needed.