I have a fantail goldfish that I have had for about a year. He (along with his two friends) live in my 20 gallon fish tank. I bought an algae eater (pleco) last week and put him in the tank. A few days later the algae eater developed red streaks in his fins and then died (about 4 days after I got him). After his death, my goldfish developed ich. I treated them for that, but over the weekend they also developed finrot. Their tales were so ragged and two of them had red streaks in their fins and on their bodies. It was really bad, and I just knew they were all going to die. I treated them with Maracide for the Ich and Tetracycline tablets for the finrot. They have improved quite a bit. They are very active and eating well. The ich has disappeared and the fin rot is getting better. However, I have noticed several black spots on one of the fish. There are a few on the underside of his belly and a few areas on the tips of his fins are black. He used to be gold and black, but his black spots went away. Are they coming back or is this a health issue. I really want to make sure they are well again, so any advice would be greatly appreciated!!!

perhaps with the addition on the new pleco, your established system couldnt handle the addition of more waste.

black marks are a sign of ammonia burns, that are healing, the black is like a scab. And i think fin rot it caused by higher nitrites. Perhaps your water levels shot up because of the new fish. Doing water changes now, more frequently will bring your levels back into healthy range, maybe 20-40% daily with aged treated water.
You want there to be NO ammonia in the water, you want there to be NO nitrites in the water, and the Nitrate level to be 20ppm or less.

The ich, i've learned is always present, but only becomes a factor when things become dirty or unhealthy. Your new fish could have brought it with him (quarrantine in the future) or with the addition of the new fish's waste and the water being affected, the ich was able to take hold.
Hope your friends feel better real soon -Tooter

black spots could indicate ammonia burns, did your ammonia test okay? It could also explain the red streaks and fin rot.

Oops, looks like I posted at the same time, I agree with tooterfish

Greetings and welcome to the board!


Tooter and mkinga covered the black spots--healing from
ammonia burns. With that, the bad looking fins are a
result in the water conditions being yucky. If you don't
have a test kit, take a water sample to your local fish
store and have them test it. Most places do it for free.
Make sure to write down actual numbers, don't get OK
or good. Like tooter mentioned, ideal water paramater
numbers would be: ammonia 0, nitrItes 0, nitrAtes 5-20
and ph level between 7.0 and 8.5.

Some questions about your setup. How big is your tank?
How many fish do you have? How often are you changing
water? Do you use a dechlorinator and temp match water
with water changes?

If you can post back with the water param numbers, we can
get your little dude back to swimming in the fast lane.

I have a 20 gallon tank with 3 goldfish. I change the water about every 2 weeks. I do use dechlorinator, but I don't temp match the water. I've never heard of that before. I tested the water this morning. Ammonia is 0, nitrite is 0 and pH is 7.6. I don't have a nitrate test kit. My other two fish have healed completely from the ich and finrot. My calico lost some of his fins, though. Will they grow back? My fish with the black spots still has them. They appear to be getting worse. He seems fine, though. His behavior is back to normal. How long before the spots should begin to heal? His tail fins are what appear to be getting more black. Should I continue to treat him for fin rot? Any other suggestions? I REALLY appreciate all of the help. You guys are AWESOME!!!!!

Bump your water changes up to once every week. Temp
matched water avoids stressing your little guys out. (think
hot shower and then the hot disapears ) The fish with
the black spots may have been affected more. Or, it may
have a calico coloring to him. If the water params stay good,
I would think after a week the black spots should disapear.

You might want to add some Melafix to your tank. It helps
with the growing and healing of fins, along with super clean
water.

He used to be black and orange when I got him. After a few months, he lost the black coloring totally. Is it possible that the color could come back? Thanks again for the advice. I will definitely follow your suggestions.

I've also noticed that my other two fish appear to be trying to nibble on my sick fishy's tail fins? Are they just picking on him? They have never been even the slightest bit aggressive with each other. The other two don't appear to be doing it in an aggressive way, though.

Black coloring in goldfish is kinda unstable. It needs lots
of light to stay with the fish. That would probably explain
why it disapeared awhile ago.

You might want to put a tank divider up so your recovering
one can do that peacefully. If you don't have a divider,
nnnnnn has a plastic mesh/grid that would work great. It's
found in the craft section. I bought a 10 pack, the uses for
it seem endless. B) The openings are big enough to let water
flow through really good. Here's a pic to know what to look
for.

Any more questions, fire away.