Is this behaviour of a Black Tetra normal?

[stu]

Hi guys, i have a small 20 litre freshwater tank, which up until last week only had 3 fish in it.

I had a goldfish, a blind cave tetra, and another fish that i'm not sure the name of, one of those small ones that goes around vacuuming everything in the tank. Last week i got another one of the vacuuming fish, and also a black tetra to add to the tank. So total

1 x Gold Fish
1 x Blind Cave Tetra
2 x Vacuumers
1 x Black Tetra

The issue is this. I have a log inside my tank, its a plastic one that sort of stands upwards and has 3 doors to get into it and a small hole on the top to get in as well, it's pretty big, not a tiny one. The black tetra just goes and sits in there all day...like he never comes out, if the gold fish or blindy goes in there he will come out until they leave and the he goes straight back in there. He doesn't seem to be very happy. When i feed them, i can literally sit there for a few minutes and watch the gold fish and blindy eat all the food and he just sits in the log. Is he going to starve? I tried to break the food up into small pieces and drop it down into the log pretty much in front of him but he wasn't interested. I was going to take it out of there and see if he moved around a bit....

Is this normal? I read on the wiki article about this fish that it needs to be kept in 26C temperature? This seems wrong to me as my LFS had these all in the same tank as the blind cave tetras and the vacuumer fish? And i asked if they were all suitable to be together and they said they were.

Black tetra - Wikipedia, the free encyclopedia

My goldfish tank is more like 16-17C temp.

Any ideas?

[Devilishturtles]

Tetras are a schooling fish which might be part of his odd behavior. You are already pushing it wish that many fish in a 5 gal tank but I would consider adding one more and seeing if he perks up a bit.

The goldfish is not supposed to be kept in tropical tanks as they are cold water fish, so you may eventually see problems with that in the long term.

[Alaris]

5gal is too small for a gold fish.

Are your "vacuumer" fish plecos? Common pleco (Hypostomus punctatus / Liposarcus multiradiatus, pardalis) with pictures / photos

If it is a common pleco then 5 gal is also too small for them. They can grow up to 1-2 feet.

Yes tetras are schooling fish and like to be in a school of at least 6, but that would be too many fish for your tank.