Killer discus

[Azazyel]

how common is it for discus to kill each other?
I have 4, 2.5 inch discus in a 20 gallon (will move them to a 55 gal, when they get a little bigger) and a small cory and a small bristle nose pleco. besides that tank is empty except for a piece of driftwood.
One of the discus has always been somewhat "not right"(not as pretty, shape not as good, more gaunt and overall looks to me it probabaly should have been a cull).
I had him in the tank for two months with two other "nice" discus and they always seem to pick on him. Last week I added a fourth discus (nice one, but a tad smaller than the other three). Everything seem to be ok, but tonight the "not right" discus is floating on his side, fins frayed, while the other discus are taking shots at him. I moved him to a quarantine tank and will see if he survives the night (he looks really bad).
Is it common for discus to kill off the "defective" ones?

[SantaFeDiscus]

I don't think its something that would happen all the time but certainly does ocationally happen. I think it is normally the weakest one that is picked on and that would include a fish that has something wrong with it. Once you pulled out the picked on one did their become a new fish that was picked on? If you think it is a cull maybe you should do just that. Sorry:(
Fred

[Azazyel]

yes after i pulled him out, the remainig two seemed to try to shoosh the new arrival away from food and such. It makes me worried that they will kill him too. The new one does appear well proportioned, well colored and fast, so maybe he will survive.
I was also worried that the problem was due to not enough space or hiding places in the tank since there is only one medium size piece of driftwood.

[SantaFeDiscus]

I would set up the 55 gallon. Add a couple of fish at a time and see if there is anymore picking on. If I am right you have 5 fish in a 20 gallon. Thats a little tight even if they are small fish. More space per fish may be all they need. You should be using the 20 for you hospital tank and the 55 as your grow out. Fish grow faster the more room they have in their tank. You may be able to put your cull picked on fish back with the others once they are all in the 55. I would medicate that picked on fish with melafix and salt. Are you medicating it?
Fred

[Carol_Roberts]

It's real common for juveniles to gang up on each other - especially when you only have 3 or 4. I'd cull the sickly one.

It doesn't sound like you quarantined the new discus, so he may "eliminate" the other two when all is said and done.

Get your 55 going. Cycle the filter and add 5 discus. After they spend 6 weeks in the 55 and are healthy you can add the 3 discus from the 20 gallon (if they are healthy) to finish growing all out.