I have two koi, one is 10" the other 12". I also have 9 goldfish, well had 4, now there's 9. the koi have grown alot over the last year, had them in a 55 gallon tank last winter. Was going to put the goldfish in the 55 gallon tank and get a 100 gallon stock tank for the koi. I have no idea how to set up a filtration system for them. Dont know what to buy or how to set up.