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I have a group of three diamond tetras in a five gallon tank, and one of the tetras keeps the other two cornered behind the heater. If they come out, he chases them back up into the corner. Several years ago, I also had three diamonds in a five gallon and this behavior did not occur, so I'm not sure if it's a function of something I'm doing differently now or if it's just due to the personality of this particular fish.

I put some taller plants in the aquarium for the other two to hide behind, and it's sort of working, but half the time when I go look at the tank at least one of them is hiding behind the heater again. Short of putting them in a bigger tank, which will have to be cycled while two of the fish are still being picked on, or getting rid of the bully, I'm at a loss as to what to do. Any suggestions?

get rid of the aggressive one and get another (or two) tetras...

problem solved...

\\\\\\\"an ounce of prevention is worth a pound of the cure\\\\\\\"

More tetras will solve this problem. They need to be in a bare minimum school of 6. A school of 8 is even more proper, and will eliminate all agression focused at the other fish from the bully.

Good Luck!

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you really think that 6 diamond tetras will fit in a 5g?

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''All the clown fish and yellow tangs in the world cant save you now!''

Actually, even THREE Diamonds is too much for a 5-gallon tank. Get rid of Mr. Nasty and limit yourself to two Diamonds (at most) in that tiny tank.

if you want a small scholl try harlequin rasboras... they will give you a small school in like 1/4 of the space... but it might be a little cramped for them in the 5g and you would definatly want some plants...

\\\\\\\"an ounce of prevention is worth a pound of the cure\\\\\\\"

Diamond Tetras need a 24" x 12" x 12" tank as a minimum size if they're going to be happy. They are among those Tetras that exhibit a behaviour I've described before with Lemon Tetras known as 'part time territoriality'. This can be seen in other Tetra species that either possess elongated dorsals (e.g., Rosy Tetras, Red Phantoms, Black Phantoms) or possess iridescent markings upon the fins (Silver Tip Tetras are a classic example). Basically, Characins that exhibit this behaviour shoal if there's a big, predatory looking fish in the vicinity in accordance with the usual "safety in numbers" rule, but if they have the tank to themselves or are among the highest-ranking fishes in the aquarium, their behaviour becomes much more individual. Males will adopt 'landmarks' in the aquarium for display purposes, spread their fins and show off like mad to the females. Rival males will be confronted for 'jousting' contests, which usually don't result in anything more than a lot of show and bluster, but which in some Characin species can result in something more serious (my psychotic Beckford's Pencil Fishes being a case in point, which started behaving more like Melanochromis chipokae Cichlids than Characins!). if your Diamonds are cramped, which yours DEFINITELY are, they you'll see that behaviour mutate into actual violence because the fishes don't have enough space. Solution: bigger tank to start with, one that will have room for 6 or 8 of them, then boost the numbers so that any latent aggressive tendencies are spread more thinly. Then, when you've given them a bigger home and a larger shoal, sit back and enjoy what jewels they can become in the right setting!


Panda Catfish fan and keeper/breeder since Christmas 2002

I agree with a couple of the others here a 5 gallon tank is far too small for diamond tetras and this is more than likely the cause of the aggression. You will more than likely find the dominant one is a mail and this is why he is so aggressive.
One belief I have is all tetras with the few obvious types not included.
Should be kept in a group of 6 or more the more the better.
Iwould really prefer to see neons or something on those lines to be kept in that size tank.

Thank you all! I moved the tetras to a 10g and added a few, and they seem to be much happier.

Oy. How many did you add? These will grow up to be fairly large fish, and you still have them in just a 10-gallon tank -- where I wouldn't keep more than 3 of them.

Well, I got two more, but they were exhibiting some fin nipping, so I kept four in the 10 gallon and moved two to the five gallon and now everybody seems to be fine...but I'll keep an eye on them and see. Ideally I'd like to get a 20 gallon setup and put the 6 tetras in there with a more aggressive fish (that won't eat them, of course) so they'll school better, but unfortunately that's a bit out of my price range right now (car trouble).

Thank you for all the help!