why is my fish also turning black?

Question
hello, chris! i found your answer to the fellow who's fish is turning black via google. i recently bought a little white feeder fish from petco. he's about an inch long, and he's to replace my recently lost 3 inch comet. because my fish is from petco, i isolated him for about a week. during this week, he started to develop black patches. i know from experience that fishes change colors-- the comet that recently died use to have black patches but turned completely orange after a few weeks or month. anyway, after i put the new goldfish in with the others (two dojo loaches and two potbelly fantails), he has turned blacker. your response to the other fellow .. oh wait.. isabella, was that he's suffering from ammonia and nitrite burns. how about the other goldfish? are they just immune to the local tapwater?

hmm.. information.. my tank has been set up for about half a year now.. it's 10 gallons... as stated above, i have two dojo loaches (one's about 6 years the other.. a year?) and two fantails (both less than two inches long)... the new guy's an itty bitty white comet... and i'm not sure about the pH/ammonia/nitrite levels... i will try to make my way to petco to test it.

thank you!
katrina

Answer
Hi Katrina;

The new fish having black on it is from recovery of a recent exposure to ammonia and/or nitrite so it probably happened in the fish store. Goldfish are kept in seriously overcrowded and often seriously under-maintained tanks while waiting to be sold. The black is like scabs healing over the damaged areas. Your other fish were probably not exposed to that.

Your tank is pretty small for goldfish really. One goldfish needs ten gallons all by itself. They get big, 6 to 8 inches in just body length alone, not counting their tails. They are messy and produce lots more waste than many other fish do. What you really need for all those guys is a 30 or 40 gallon tank. They may be "kind of" okay right now, but they are growing and it won't be long before they make such a mess in there that it will not be possible to keep it clean, so they will get sick. In the meantime, make a 25% water change once or twice a week and be sure not to overfeed. And....shop for a bigger tank! That's the fun part! I'm always up for an excuse for another tank myself.  ;-)

Here are some web pages about goldfish and what they need;

http://www.kokosgoldfish.com/care.html
http://www.goldfishinfo.com/setup1.htm
http://www.petlibrary.com/goldfish/fishcare.htm
http://www.aquariumhobbyist.com/articles/Goldfish.html
http://www.flippersandfins.net/goldfishcaresheet.htm

At Your Service;
Chris Robbins