My goldfish is getting black marks on his body?

Question

I have a comet in a 29 gallon tank and he is about 2.5 inches long. A few days ago he started getting black marks on his body. It thought it was his color changing, but today he started to act really weird. He is kind of just swimming in one spot and then sometimes he darts around the tank super fast. WHAT IS WRONG WITH HIM PLEASE HELP!! I am going a partial water change right now. PLEASE TELL ME WHAT ELSE TO DO. I rescued him from the feeder goldfish and I got him for 29 cents and he is really cute and I don't want him to die. Thanks.

Answer 1

Black marks are usually a sign of ammonia burns, the black is the healing stage.  Definitely do the partial water change, and be sure to do them frequently.  Get yourself a test kit, preferably not the dipstick kinds because they suck, and make sure your ammonia and nitrites are at 0 ppm, and nitrates under 20 ppm.  

If this is a newly set up tank those levels will be off, and I would suggest getting with someone that has an established and disease free tank, and using some filter squeezings from their filter and add it directly to yours.  If that's not possible, get some Prime by Seachem, and add some of that daily to the tank until it finishes the cycle process.

Also, since he's a feeder, they're usually not very healthy.  I would suggest going a round of medicated food as well-both antiparasitic and antibacterial food.  I just picked up 2 feeders a few weeks ago as well, and automatically medicated them both internally and externally for bacteria and parasites.  Definitely won't hurt.

Answer 2

not sure sorry

but when he gets older he will need a 50 plus gallon tank

unless he is a fancy goldfish

Answer 3

Yeah, man. My goldfish got some black marks on it, and my mom said it was just his pattern, but then the other got it, and soon they both died. GO TO A VET!!!!

Answer 4

You better get it checked out by a vet ASAP...Our fish had a similar problem and the black marks spread to the the other fish that were originally fine. I think its possibly due to a fungal issue or something like that...