My father-in-law recently gave my wife and I a 20 gallon aquarium that came with a koi (it is a koi, right?) that is about 6 inches. While the aquarium may be able to support the fish (using a general surface area rule), I intuit that the fish really should be in a larger aquarium or pond.

I've had aquariums in the past, but this fish seems to swim quite fast for the limited area he has to swim. Is this an indicator of stress? To make matters worse, it appears that the fish has several diseases. The most apparent disease (or maybe it is a result from mistreatment) is that there are many scales on the fish that appear to be missing, but when the light hits them just right, it looks like they are all there. It's almost as if the scales are transparent have not retained their shininess. Also, on its right fin where it meets the body, there is a bumpy sore. Furthermore, on a few of the transparent scales and looking closely at the fins you can see small capillaries that didn't seem to be there when we first got the fish.

I've checked the ph of the tank, and it seems to be on the very low end of the scale (acidic). I've changed half of the water once (the ph of our tap is neutral) but seems to have had no effect on the aquarium ph level. Could the low ph be causing these diseases? Can ph be corrected? What can I do to address the individual diseases?

I would like to be able to sell or give the koi away so that I can put more appropriately sized fish in the aquarium, but I figure I will have a hard time getting rid of a fish with diseases. Moreover, I feel kind of bad not being able to help heal the fish. If the fish does regain it's health, how do you recommend I get rid of it?

Here's a picture of the fish:


Here's a picture of the fish in the 20 gallon aquarium:


I apologize for the quality of the pictures... my wife's camera is not that great. Anyway, thanks for your time and I hope you can help!

Well to help the Koi it should be in a lot bigger tank then the 20 Gallon. You should also clean out the tank at least 2 times a month maybe more Koi are like Goldfish and produce a lot of waste. He does look unhealthy but with the proper environment he should be fine. Also in the spring, you could make a Koi pond (if you have a yard) they are really pretty.

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James
from Queens, New York

So theoretically, if I keep him in the same tank and ensure that the tank is cleaned regularly, his health will improve? Cleaning the tank regularly will solve my pH issues?

And, theoretically, his health should improve to the point where he visually looks healthy? What about those transparent scales? Is that permanent damage?

As my ultimate plan is to give the koi away or sell it, do you know a quick way to do so? Do pet stores commonly purchase pre-owned fish?

With a koi you will need to change that water at least a couple times a week. But the small tank isn't going to help the stress he is in from not enough room to swim. I would find someone with a large tank to use as a hospital tank to get him well enough to put into a pond. Koi should never be kept in tanks except for maybe over wintering where it would be to cold for him to survive.

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Actually some pet stores would take in more mature fish.

About the scales I do not know if they will grow back.

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James
from Queens, New York

Well, thank you both for your replies. I agree that the koi needs to have more water for a home, and I am actively looking for a new place for him. Unfortunately, I still don't know what the diseases are or how to treat him, but I am now changing the water more frequently and trying my best not to stress him further. Hopefully in time the pH level will become that of the treated tap water, and his diseases will heal over time. Thanks again, and wish me luck!

So, after some more researching I realized I had a very large goldfish, not a koi. Surprise!

Anyway, after more frequent water changes he seemed to be less stressed and the red veins disappeared.

I made a trip to a local pet store and they said they would take the fish... missing scales and all. When I brought him to the store, they assured me that he would find a good home and I could get a free replacement if I wanted. Of course, I declined.

Was it really that easy? At any rate, I recommend talking to a local pet store when you have a fish you want to get rid of. If your store is anything like mine, there's a good chance they'll take the fish, and maybe even let you exchange it for another one.