Many thanks to all for the responses. I will continue
to monitor my butterfly koi, and if/when it gets too
big for the present tank, will either move it into
something much larger, or trade it. I suspect the
local koi retailer will have some suggestions.
If mine grows like one of Jan's, I don't think I
want to contemplate a 5000 gallon tank!

Gail
near San Antonio TX