More toxic at higher temperatures. Is mutagenic, teraogenic. May be toxic to some species if overdosed. More toxic at higher temperatures. Formalin may disrupt biological filter.
Doses are in active ingredient.
Merthiolate paint on wounds disinfectant, fungi, bacteria rinse fish before returning to tank. Do not get into gills. Harmful to biological filter. Will stain hands and fabrics. Effectiveness reduced by organics in tank.