Please help a beginner with diamond tetra agression

I just started stocking my first tank, 29 gallons, fully cycled. I bought nine harlequin rasbora and 6 diamond tetras. My problem is that one of my tetras (the biggest and most beautiful one, of course) is harassing all five others. He pretty much leaves the rasboras alone, but he patrols the entire bottom of the tank and chases away any of the five that venture down below the top third. I now have 14 fish sitting at the top of the tank and one mean (but pretty) fish at the bottom. What can I do? Will buying another tetra or two help, or just exacerbate the problem? What about seeing if I can return this one problem fish and exchange it for another (hopefully less of a bully)? Thank you.

 

Seems like you just have a bully. How bad is he? Does he physically hurt the other fish, or just chase a split second then peel away? Usually LFS will allow you to bring back fish that are problems, I did this with Colombian tetras. Does the tetra let other fish eat? That is very important.

 

Welcome to fishlore. =) I personally wouldn't chance adding more tetras. I'd return the bully and see if you can get a calmer one.

 

He doesn't seem to be hurting them (at least I haven't seen it yet), and he does let the others eat. In fact, feeding is the only time when he gets too distracted to bother everyone else. I have started feeding twice a day after I read that it sometimes helps if the fish are a little less hungry. I had been hoping he would settle down, but it has been about six days now.

 

If he isn't hurting anyone and none of the others are showing signs of extreme stress (losing color, playing dead, etc) I'd give it another week maybe. Typically I'd say you need to get a bigger group...but you have a fairly decent sized one now. I'd give it a few more days to a week and if it doesn't calm down either try to add a few more, or rehome him (with rehoming him being my preferred option).

I had a similar issue with a single lemon tetra one time. He ended up turning the entire group of tetras aggressive and they destroyed a couple of guppies.

 

Yep. Add more. I had the same experience with Bleeding Heart Tetras, Serpae Tetras, Tiger Barbs, etc. it sounds counterintuitive, but a bigger school helps calm the Alpha down.

 

what sexes are the other five? If all males, he doesn't want more males in his territory. I have often seen groups in the store that were almost 100% male.

 

Thanks for your ideas (just in case you were keeping track, it's two votes for getting rid of him, one vote for getting more, and one vote for waiting it out!). My fish store doesn't seem keen on taking him back, but interestingly, I got 3 juliI corys yesterday (I will get more, but the store didn't haven't them), and that seems to have calmed things down some. Maybe he realizes he can't have the bottom of the tank to himself so he has given up trying? It's not perfect, but it does seem like an improvement.