how old is the tank? does it get any sunlight? brown algae is normal in the first 6 months of a tank's life. not sure of brackish live solutions, but just keeping on top of it will make a big difference. tank maintenance, water changes, scrubbing, less light is often the best solution.
unrelated to your post, but dwarf puffers are freshwater puffers. if they are true dwarf puffers then you really should find a way to move them to a freshwater species only tank.