This Kohaku is bred by Marudo and will be staying another year with the breeder. At nisai it's about 55cm to 60cm. Hisashi says that this Kohaku should reach about 70cm by next harvest.
Filters that have not had water circulating through them for the winter should be cleaned well before turning the pump back on this spring. Cleaning will remove toxins that can develop from waste breaking down in the filter in the absence of oxygen. Once your filter is up and running, seed it with beneficial bacteria.