Why is my cory swimming against the glass?

Interestingly enough fish can not tell their reflection from another fish, my corys tend to try to get into the background thinking its open water, also if you notice yoru corys have two "nostrils" and will dart up to the top of the water and suspend their heads above the water, why? because tehy can breath air using a laberinth organ like guoramis or bettas.

I'm serious man all fish do this. I have a 30 gallon tank lke you do and My tiger barbs don't do anything BUT this. The whole day they follow their reflection on the glass. From the inside of a tank theres alot of reflection.

I'd say he's got an infection and you better get some medicine quick. A good tropical fish store could tell you which virus he has and what medication to put in the tank.

all fish do this, it's just a game they play i guess. My gold barbs, my betta, and my ram cichlid all do this, but my barbs go real fast to the top of the water, lift a bit of water from the surface and shoot back down, it's not anything to be worried about. This fish is probably just more active than the others.

hehe, It's just the way that they swim/school when they are happy. I have a shoal of 3 also and their swimming behavior is what makes me love them so much.

I'm trying to order more, julii corys are pretty rare where I live.

They will swim a ton more like that when they have 6 or more in their shoal (group). Its just the way they travel. They will often replicate exactly their shoal mates' movements. =D

They will eat algae clinging to the sides, as well as gather oxygen bubbles that adhere there as well, also if they notice you feeding them they may be trying to get your attention for food, but they dont always need food when they do this, so don't overfeed because you think your fish is begging.

I have seen this other corys too. I think he is looking for food. I have seen it also if there is a lot of water movement in the tank. I read an article that said they do this when there are ready to breed. read the fifth paragraph of this link.

http://www.articlefishtalk.com/Article/Breeding-Th...

lol i used to have a cory cat and a chinese sucker in my community tank with a few others.... they were hillarious. both of them did that, constantly..... first, one would chase the other, then the other way around, it was great. they lived long healty lives...... i wouln't worry about it, he's probably just playin.

good luck!!

Most likely it's just attracted to it's reflection. Changing the lighting may help.

my gourami does this and it's quite healthy. It's probably just a particularly active fish. Don't worry at all.