This is a discussion on Shubunkin and tankmates? within the Cyprinids and Atherinids forums, part of the Freshwater and Tropical Fish category; -->
I'm redoing my 70g.
So far, I know I want
2 Shubunkin Goldfish
3 Feeder Goldfish
Snails (What breed do I get?)
Two shubunkins is pushing it but okay; however, the additional feeder goldfish are overstocking and overcrowding the tank. Five 12-inch fish in that tank would not make for happy anyone. The common pleco might be okay, but I have very little experience with their bioloads aside from knowing they are large. The one thing I will know you need is some major filtration. A canister rated for a tank double that size. I wouldn't do HOBs with goldfish in anything larger than a 55 gal.
As for snails, with goldfish you are going to have trouble keeping any alive. I've had the best success with Malaysian trumpet snails as they burrow, and with all the waste that goldfish make, they rarely come to the sides for food. Apple snails would be good as they are usually too large to fit in a goldfish's mouth and they require the same hard water that goldfish do. However, they aren't great algae eaters, and you will have to feed them separately which is going to be hard with goldfish around.
For plants, you're going to want fast-growers. These will help suck up the massive amounts of ammonia that will be present in that tank. Hornwort is great as it does wonderfully in the hard water that goldfish need and it grows like mad with the right light. Leaving it floating will allow it to get a good amount of light. Vals are also pretty good with goldfish. And the tough leaves of the anubias plants are also great. Goldfish will typically leave them alone. Plants and goldfish are a balancing act. Some goldfish are ravenous vegetarians and some are not. It's basically trial and error to see which (if any) plants your goldfish will allow in the tank.
I would never put a larger koi type goldfish in an indoor aquarium unless growing out for a pond. They are very dirty fish
Why not look into fancy goldfish if your looking to go that routs? Thrn have golden dojos and white clouds
Koi should never be in fish tanks, but in the proper setup you can keep single-tailed goldfish. I have seen it done before. Shunbunkins are the best suited for it as they tend to stay a little smaller. But I do agree that fancies would fare better in a tank than single-tails.
As far as goldfish with dojos and WCMM: dojos get about a foot long and need a 4 foot tank. In this size tank they could work with fancies, but I've had incidents of dojos eating the slime coat of my fancies. They also need to be kept in groups of 3 or more like most loaches. This will decrease the number of other fish that you can have in there. WCMM will most likely become food for goldfish. They are best in a tank without goldfish.