My first LFS
also recommended frozen brine when I got my first fish and I had nothing but problems. My Damsel wouldnt' eat it and I believe that it did help feed an outbreak of Cayno.
My new LFS
recommended flake and all is well. Both of my fish take it (Dottyback and Damsel) and it is much easier to control portions. I do, on occasion feed the brine to them as a treat.
in the future, I will also try anther frozen mix, Formula One from Ocean Nutrition. I heard that this is pretty good and I heard that mixing up what you feed your fish is a good practice.
I am a newbie....but this is what I have learned so far...