Remember to be consistent and particular of your salinity levels.. There is a different type of nitrifying bacteria for each salinity level, and too sudden of a shift in salinity can kill off all that good bacteria. So make sure you use a system for water changes and measuring salinity levels.
I killed some brackish puffers, doing too large of a water change and not paying attention to the shift in salinity. After the next feeding, an ammonia spike occured. Ammonia is more toxic in a higher pH, and the brackish tank being at 8.3pH, ended the puffers quickly.