Goldfish Problem

[Kales]

I have 2 goldfish, I've had goldfish since I was a child, but I don't know much about them at all. I know I have to feed my fish and keep my filter running. A few days ago my filter stopped running. The water got pretty bad before I could get it functioning again and there was some black gunk in the corners of the tank. I cleaned my tank immediately, but one of my fish has black stuff lining his mouth, eyes and some on his fins. He seems sluggish. What do I need to do to get him clean and healthy? Please post here or email me at as soon as possible.
Thank you,
Kaleigh

 

[Butterfly]

What size is the tank ? what are your water test readings (ammonia, Nitrites, Nitrates) . If you haven't done so a large water change is in order. Goldfish are large waste producers and the tank readings can go bad fast.
Carol

 

[Kales]

I don't have tank readings I'm sorry. Change the water again? It's a 10 gallon.

 

[Butterfly]

The recommendation for goldfish is 20 gallon for the first and 10 additional for the second so as we can see your tank is overstocked. As soon as you can you need to get some water testing supplies. The liquid kind gives a more accurate reading. I believe petsmart has a coupon you can copy on their website and take to their store for aquarium pharmaceuticals brand which makes it much less expensive.
Since they are in a ten gallon tank, lets work with that Goldfish are huge waste producers so they will need at least a 50% water change about twice a week to keep them healthy. Vacuum half the gravel at each water change to get the waste and any extra food that might fall to the bottom out. Keep us posted
Carol