So this is a combo introduction/question thread. Hey guys! I've been searching for a decent goldfish orientated forum for a while now.

Anyway, here's the deal.
 
I went out to my pond today, and I noticed a tiny little white fantail flailing around near the surface. I certainly hadn't put him in there, and a few hours later (after I fished him out) I noticed some kids climbing over my wall. Apparently their mum told them the fantail had to go, and they realised there was a neighbour with a pond and all fish love ponds, especially when it's 5000gal 
(my wall isn't easy to climb over; I'm impressed they managed to get a fish over it.)

I decided to keep the little guy, and he's in a 3gal. I know that's not a great size for a goldfish, or most fish in fact, but it's all I had spare. He can't stay in the quarantine tank forever though.

Health wise, he doesn't appear to have ich, nor are there any signs of fin rot or other fin damage. Comparing him to other fantails on the internet, he looks pretty normal. Still he's in quarantine for the next two weeks regardless.

My other tank is home to two fish, a common and a comet. They've been a healthy pair for a good five years now. The tank itself is a long 85gal, and planted. The comet is surprisingly mellow for his species; I understand most of them are hyper little things, and the common is your typical common.

On the assumption that the fantail survives, could he be introduced into the tank with them? I know one issue will be that he'll be unable to reach food as quickly as the other two, and I'm already looking up ways to avoid that, but could owners of other fantails help me out with their suggestions? Or will the other fish just harass him to death, and I should just shell out for another tank?

I've never owned such a stumpy fish before, but goshdarn is he cute <3

He wouldn't fit in their mouths at all; I guess he's nearly fully grown.

Something I have noticed now is that he's kinda sluggish; is that an underlying health concern or are fantails normally slow moving?

He's survived the night, and he's zipping around like you said he would. I think he could make it 

Yeah, it's filtered; the filter's one of those immersed ones, and it's built for a tank twice the size so I think it'll do its job. It also has a little bubbling thing, so I guess the water is aerated. Goldfish are so messy -.-

I know 3gal isn't ideal for a goldfish, but like I said, it's only temporary; I would have set up and cycled a bigger quarantine tank if I'd been expecting his arrival in advance.

I'm changing the water ~25% every day, and so far nitrate levels have remained at zero. I also picked up something at the LFS that claims to reduce nitrates, so if levels suddenly change I could try using that at the same time.

I get the feeling he'll be fine with my pair; he's looking so much healthier then he did when he was in the pond. He's eating as well (the bloodworms went down a treat), and just now he chased my finger along the wall <3

Thought I'd finally update; the fantail survived, but has yet to join the big tank. Why?

Ich decided to pop in for a visit. Ugh. I've got about a week of treatment left to do.

It's not him, it's the pair in the big tank x3 Which makes it even more annoying, because the chances of the little guy contracting Ich regardless when I do eventually put him in are really high >.>