Sick tetra

Question
I have a 20 gallon tank that seems to be healthy.  I have had 5 neons living in the tank for 10 months.  I have 3 black skirt tetras and 3 other tetras that I don't know what they are.  One of the black skirts I have had for over 6 years and now has bulged eyes and seems blotted.  It stays close to the top of the tank where all of the other fish stay mid to low part of the tank which has always been normal.  It seems to be distressed.  I change 20% of the water and only use filtered water with change.  Everyone is healthy but this one.  Of the black skirts he/she is the oldest.  The other two were introduced the tank 10 months ago.  All have been healthy until now.  What is the life expectancy of the black skirt?  Is there something I can do to help this fish?

Answer
Hi PJ,

The average life span of this sort of tetra is about 5 years, so you've done an exceptional job keeping it alive! Tetras like to school, so you should try to add a couple more black skirt tetras if you can - depending on what the other tetras are, you might not have room.

I don't think you can do much for it except optimize water quality, and maybe add more circulation by adding an airstone or placing a low flow powerhead towards the top of the tank. More circulation is always better, it keeps the water healthier to have more dissolved oxygen. It distributes the heated water from the heater more evenly. Provided it's not incredibly turbulent, fish appreciate more flow and it keeps detritus from accumulating at the bottom so much.

You might want to check your water with a test kit. A pack of 5-in-1 strips (25 to a pack) is only about a little over $10 at Walmart here, and it will give you readings for both water quality (nitrite and nitrate) and water chemistry (pH, alkalinity, hardness). Just make sure that the water chemistry of your tap water is about the same as your aquarium, and that your nitrates are not too high - under 40 ppm is recommended. All aquariums acidify over time...when an aquarium has been established for a while, the pH tends to get low and the nitrates tend to build up. Doing a few big water changes should help, just try to get the nitrates down if they are high, and watch the pH.

Other than that, if your fish is eating, I would just let nature take its course. If it seems like it can't eat, I would euthanize it humanely, since starving to death is a painful way to go:
http://www.wetwebmedia.com/euthanasia.htm

I hope that helps, take care.
Nicole