Did I blow it?

Serpae Tetra

As this is one of the most richly colored tetras, it would reason that it would be one of the more aggressive of the family. This is not to say that you can't keep them in a community setting, but you do want to choose their tankmates more carefully. Neons and Cardinals are out of in that they are smaller, and they will be hounded by the Sepaes relentlessly. Many look-alikes are often sold as Serpae.
The Serpae is not a giant fish by any stretch of the imagination. The larger of the genders, the male, seldom exceeds an inch in size, but never the less seems to have a Napoleonic complex when it comes to its meeker tankmates. Despite this smallish stature, its crimson coloration within most of its body gives this little guy a more imposing presence. This fish likes to school.
You should have consulted with some of the members of the site before
you do any impulse buy I think your tank is definatly overcrowded now. 20 harliquens is way over the top for an already stocked 20 gal throw in the Serpae and the peacefull community setting all of the suddon turns into a struggle ...
:rant: :rant: :rant: :rant: :rant:

So all "richly colored" fish are more agressive?

Maybe if you add more Serpae Tetra they wont be so aggresive because they are in a bigger school. Or you could take them back? I think he thought you had them in a 20 gal.

When I stocked my first tank, I had no idea about schooling and aggression. I just bought a couple of this and that. It's a 20 gal and it consists of 2 swordtails, 2 danios, 2 white skirt tetras, 2 platys, and 2 serpae tetras. I had no trouble at all. Then I added 6 neons. The serpaes chased them for about 3 days, I made sure the neons had hiding spots, and now it is a wonderful community tank. I do wish I had larger schools of each, now that I know better, but my point is, my serpaes are fine, they even leave the neons alone now.
I'd give it a few days. You sound like you have lots of hiding spots and the tank is big. See how it goes, and if worse comes to worse, take them back and explain what you did. Maybe they'll exchange them for something you like better.

He can't CATCH them to take them back!

Aqua, do you have a piece of plexiglass or some solid 'wall' that would be safe to put in the aquarium? Maybe you could try to wall off at least some of the Serpaes to attempt to catch them? I wish I could be more help. Best wishes!!

Poor you! I tried serpaes out once and found they were too agressive. Some people seem to hit on the right combination of fish and tank size and have no trouble, others (like me) end up with teeny pirhanas.
One little trick (if you need to get them out of your tank to take them back) that worked for me once was catching fish asleep. In the morning, turn on just enough room light so you can see, and be prepared to act quickly. Leave the aquarium light off. Before the fish wake up, you can sometimes sneak up on them with the net. You won't likely get more than one or two chances before they wake up completely, and it may take two days to catch all four, but it's worth a try if they're driving you nutso chasing your more peaceful fish.

Usually they're not a problem at all if kept in schoal (for me anyways)

g/l with catching them though, maybe a larger net would help ya

if you have or can get two nets
then chase with one and trap with the other tis worked a treat for the guy in lfs
may be worth a try

and i am going to buy a book idiots guide to fish breeds for beginners (any suggestions) dont fancy making the same mistake.

good luck hope you work it out