black border on goldfish tail?

[goodfish42]

My goldfish's tail has suddenly developed a black edge -- the end of his tail is dark for maybe half a millimeter. I think the very tips of his pectoral fins are dark too. What could this be? The other fish is fine.

Tank parameters (ppm):
nitrate: 20
nitrite: 0
water hardness: 25
alkalinity: 40-80 (hard to tell the difference on the test strips)
pH: 7.2

These parameters have been stable since just after starting the cycling.

Also I checked the ammonia today, and it was 0-0.25 ppm (again, test is hard to read).

Temperature varies a bit over the course of the day, from 75 F to 78 F or so.

Tank is 12 gallons. Cycled for about a week, has had the two goldfish for about a week. They're little goldfish -- I know when they get bigger they'll need a larger space. Right now they're about 6 cm long each.

Filtration: Bio Wheel - comes with Eclipse System 12 tank. Box claims 150gph.

5~How many fish are in the tank? What kinds of fish are they and what are their current sizes?

2 goldfish, 6cm each.

6~When is the last time you did a water change and vacuum the gravel? How often do you do this? How much water do you remove at a time?

Haven't done this since setting up the tank almost a week ago.

7~How long have you had the fish? If the fish is new, how did you acclimate it/them?

I've had the fish for about three weeks now I think.

8~Have you added anything new to the tank--decor, new dechlorinator, new substrate, etc.?

No, just the stuff that was in there while the tank cycled.

9A~What kind of food have you been feeding your fish, have you changed their diet recently?

Feeding them goldfish flakes (Top Fin brand) and occasionally sinking granules (Tetra brand). Gave them some freeze-dried bloodworms yesterday.

Any advice?

[Devilishturtles]

Any chance for a picture?

A color change in goldfish is very normal. It's just what they do. If the color looks like a normal coloration, I'd not worry too much. Your orange goldfish could end up white, you just never know. All goldfish are born brown, by the way. They develop their color over time.

Also, try lowering your temperature to around 72-75F. They'd be happier with the cooler water.

HTH

[goodfish42]

Any chance for a picture?

I tried for a picture but my goldfish (his name is Jean Valjean) gets so excited when I get near the tank that he swims right at me and I can't get a picture of his tail. The best I got were blurry photos that didn't show enough detail.

Also, try lowering your temperature to around 72-75F. They'd be happier with the cooler water.

Is there any inexpensive way to lower the temperature of a 12-gallon tank? I think my room temperature is something in the low seventies, maybe higher, and I can't control the thermostat.

[Zagz]

Try having a fan blow over the top of the tank to cool the water and leave the lights off a bit more during the day. I agree goldfish change colors, I have a smaller goldie (4") that was mostly orange but has a black streak all the way down his back for the last couple of months.

[jsoong]

Another reason for black fin edges is healing.

Injured fins (mechanical, or chemical - such as an ammonia burn) turn black during healing. Perfectly normal, and will disappear over a week or so.

If you have a calico, the black can be normal coloration as well. Calicos change colours as they age, and they have a limited ability to control their body colour as well. They can almost eliminate the blacks when placed in white background, and have more black in dark surroundings.