Do water changes with RO water to get rid of phosphates and nitrates...Also, brine shrimp isn't a very good staple for your fish unless it's soaked in some kind of vitamin or spirulina or something. There's little nutritional value to it. I fed my purple tang brine shrimp for too long and he lost his color, now I'm feeding him New-Life Spectrum Thera-A and Formula 2 pellets and he looks amazing! Learn from my mistake, haha.