No, cories and goldies don't mix for the reason debnal wrote, although water cleanliness shouldn't be the factor because goldies will not foul water any faster than than any other fish of the same bulk: the operative word being- bulk. Not just length, but total bulk- weight per fish.

It's temp. Cories are tropical and goldies are not. Your cory is indeed stressed and unlikely to survive in the conditions you described.

However, your cory is stressed for another reason: they are schooling fish and don't do well unless kept with others of their own species. 6 is the least I ever recommend, but 4 would be the absolute minimum per individual species.

Birdwidow and I agree, it appears, only on the water temp. I have had single cories that lived long lives - in aquariums with other non aggressive tropicals. 3 goldfish in a 5 1/2 gal aquarium most certainly does have water quality issues. You have indicated small, but a small goldfish can be 3-4 inches long (relative to their adult size), and that is an issue I didn't address in my first post as it was not the point of the question. A single adult goldfish at minimum needs a 10-20 gallon or larger tank, so I fear the 5 1/2 gallon tank with 3 goldfish will not support them very long as well.

Thanks for the advice. By small, I mean they are all less than 2" in size (not counting their tails). I also do 25% water changes every 3 days or so (I just take water out of the aquarium to water the houseplants with), and the water is never cloudy. I also check the water temp fairly often, and it seems steady at 75F at day, dipping to 70F at night. The tank is in the corner of our apartment with the heating vents, and the tank bulb seems to help heat as well. I do intend to buy a larger aquarium for them within the next year, but they haven't really grown much at all in the several months I've had them. Thanks again.

Nick, the 25% water changes certainly do help in keeping the water conditions better - do you also vacuum the gravel when you do that? If you were to go by the 1" per gallon rule, which is really intended for slim bodied fish, then your little tank is already overstocked. Now consider that goldfish are not slim bodied fish, you are even more overstocked. The fish, once you have provided them larger quarters, will grow more. They are probably a little stunted because of the cramped quarters. I have 3 which are each 3" not counting the tail, that spend the winter in a very large rubbermaid type container. They inhabit my 60 gallon outdoor pond when the weather warms. If you decide they need more space until you can get the larger aquarium, you could use a plastic container. They would probably enjoy the extra room. And goldfish are alot more fun to watch from above rather than from the side - that's just my opinion tho. Meanwhile, you might check wetwebmedia.com for the best accommodations for them once you decide to give them a bigger home. Hope your cory does ok, or you find him a home where he can be a happy fish. While your water temp seems to be in the right range for him, the fluctuation of almost 10 degrees from morning to night could also be causing him some stress. And even though I have kept cories singly, they really are happier in a group of 3 or more. Consider this: Move your goldfish, as you will need to anyway, get another cory, and possibly 1 or 2 small colorful fish like male guppies, platies, cherry barbs for the 5.5 gallon.

Ahh the wonders of Pet Stores and bad advice. You have heard all about over stocking with the goldfish, and you are trying like crazy to keep up with the 25% PWC every four days, but without good filtration, ample heat 78, and a variety of foods this wont work out. I do however have a suggestion for helping your Cory to get a chance to eat. What you need to do is to creat a space that only the Cory can get into, and thats where you keep its food. Its going to have to be pretty sturdy since your Goldies are going to be going nuts when they CANT get to that food. I have used a plastic tub with small holes cut into all four sides with a very stout, stable rock kept on top. I would also suggest you try sinking shrimp pellets, mine love 'em.

I have a 30 gallon tank with two goldfish and one zebra corey. They all seem quite content. The corey swims around along with the goldfish. Usually where ever they are, the corey is too.
I also want to comment about somebody saying be suspicious of petsmart workers. I don't think that is true for all of them. One in particular in the petsmart I go to is so knowledgable on fish. He never "tries" to sell me anything. So I'm just say in', don't judge all by some.

I have had tanks since my sophomore year of high school (I'm going on 37 next month.) I have never had anY issues with keeping cories and golds together. Cories prefer a temp of 60 to 75 degrees, although they can tolerate up to 85. I keep my goldfish tanks between 75 to 80. Both types of fish are perfectly happy. As long as the space and water quality are good and everyone gets enough food, everything is just fine. I would avoid younger cories with older golds, however. They get quite large and will eat anything that fits in their mouths.

I'm new at this fish stuff but I have two fancy goldfish and one small Cory cat and I was having the same issue and I discovered my catfish was just picky he didn't like tablets he likes shelled peas and cucumber try that

I have two green Cory catfish in a 29 gal tank with two medium sized goldfish and one large. Until just recently they were all in a 15 gal tank. They have been together for 21/2 to 3 years and do very well. My oldest Cory is 9 or 10 years old. They eat the goldfish flake food, shrimp pellets, and bottom feeder pellets. My water temp is between 70 and 78 degrees. I do bi-weekly water changes.

Your corey is a night feeder and he will come out mostly at night you need to turn the lights off after 12hours of continual light , even plants require darkness.so the fish can be nocturnal

I have just trnsfered to a 10 gallon tepid tank 2 bronzies and 2 adult corey.Waiting on any behavioural changes .Bronzies love the extra space. So do the Corey.

I have 7 goldfish and 4 corys in a 4 ft and all are doing perfectly fine ! my corys eat my goldfish food !