The dose is dependent on water volume, not fish size. Remove the fish in its pond or tank water into a suitably small container. The fish itself pumps the drug across its gills, administering the dose till effect. You must watch throughout and remove the fish when it is suitably anaesthetised.
For a quicker knockdown you can increase the dose, but always watch the anaesthetic process, temperature and species of fish will cause some variation in speed of anaesthesia.
Use at a rate of 1 pump per litre of water (or 0.5-0.7ml per litre, 500-700 ppm).
Return the fish to untreated water for recovery following the procedure.
Aqua-Sed can be used for euthanasia of fish. Confine the fish in a small volume of water in a suitable container and add a four fold dose of Aqua-Sed (2000-2800ppm). Leave the fish quietly for an hour, at which point it will be dead. Dispose of the fish appropriately. Some owners do this process in a plastic bag, and after the hour, freeze the bag until it can be disposed of appropriately.