yup, thats the cause right there...
i have more fish than you and i feed much much lesser
fish do not need that much to eat,
let them graze on the LR...
feed your tangs nori, maybe half a cube of BS to supplement?
once a day? twice on sundays and public hols
there should be no leftovers,
i'd rather they be not so full than have food rotting in the tank
thats a lot of skimmate!
you can try tuning to get dryer skimmate
open it and clean it,
bet you its full of detritus, if possible wash with salt water
you can try setting up a refugium,
it has many benefits.
try reef safe hermits,
or ceriths or nasarius snails.
or a brittle star