Formalin has been used in aquaculture for quite some time. Others deserve credit for much of its use. 7 to 8 years ago when we first started I would not accept the answer that ammonia was the cause of seahorse fry scratching. Frank Gangi was the who suggested that it was protozoa irritating the fry as the cause and suggested formalin. Abbie was the one who experimented and developed the our protocol which we have been passing on for some time. Her protocol varies among the species.
We are searching and experimenting for ways around this as formalin has some safety issues with humans, is becoming difficult and expensive to get and I believe there has to be another way of accomplishing the task.
Dan