Congo tetra tank mates

[Scott_T_27]

So I just added 5 congo tetra to my community tank last week and they have decimated my tank. Harassed to death 15 tetra (cardinals and white neons) and 5 harlequin rasbora. I thought they were supposed to be peaceful? I didn't think it was them at first as they didn't seem to be harassing any other fish until I caught them in the act this morning. I thought disease had got into my tank somehow, but no just the congo bullying anything smaller than them.
Been told if I add more they should chill. Looking at the ones I have now, I've ended up with 4 males and 1 female. I want to keep them as they are awesome fish but wondering what kind of fish would be best to keep with them so I don't have another mass death on my hands. I hate losing fish. Some of the ones they killed I've had for years. I'm gutted.

 

[Colin_T]

What are the tank dimensions (length x width x height)?

What is the GH (general hardness), KH (carbonate hardness) and pH of your water supply?
This information can usually be obtained from your water supply company's website (Water Analysis Report) or by telephoning them. If they can't help you, take a glass full of tap water to the local pet shop and get them to test it for you. Write the results down (in numbers) when they do the tests. And ask them what the results are in (eg: ppm, dGH, or something else).

 

[GaryE]

They should be in a minimum 4 foot (1.3 metre) tank, with a good flow. In nature, they like moving water. They love a disturbed surface that gets hit by morning sunlight.

Ideally, they should be housed with fish their own size that also like to run in the current. They are often sold small, but be aware of their adult size.

They do well with many rainbows and mid-sized barbs, although some barbs will trim their tail filaments if the barb group isn't big enough.