Usd Catfish

[Jbram]

Ok so I have the small school, if you can call 3 a school, of upside down catfish.  The one with the popeye is all healed up and doing well.  Now I am concerned that the largest of the three may be somewhat predatory and am curious to get some feedback on this.  The research I had done suggested these cats make good community fish.  I have noticed when the larger, he is about 2 inches, comes out of the cave he can be somewhat aggressive in that he tends to chase some of the other fish around.
 
The fish he chases are his size or slightly larger.  Here over the past day or two I have noticed a couple fish missing and have only been able to find remnants of them which are mostly eaten. The latest is my male Praecox Rainbow.  I have a 120 gal. tank planted with 4 quarter size angel fish, 12 tetra, 6 harlequin rasbora, 1.5" BNP, 2 in rubber lip pleco, 5 panda cory and 5 bala sharks and 2 females Praecox Rainbow.
 
I do not see signs of aggression from my other fish this is the only one I have seen behave this way at all.  The other two USD cats seem mellow and come out during the day and hang out with everyone.  The large one stays in his cave and only comes out once all the lights are out.

 

[ncguppy830]

first the balas need to be rehomed as that tank is to small. But as for the usd there is a larger version the giant or black usd that is aggresive, you may need to post a pic .what was your rainbows size?

 

[N0body Of The Goat]

Are you confident that all 3 USD catfish are the same species? Many Synodontis will spend at least part of the time swimming upside down, but the very social S. nigriventris and S. contracta spend almost all their time inverted (unless feeding off the tank floor). Some less social synos can be mislablled, such as nigirita and euptera, which grow far bigger and have been known to attack tankmates.

 

[Jbram]

I have been trying to get a good picture but due to his anti-social behavior I have had no luck so far.  The two smaller cats have darker markings more like bands that are closer together.  The markings on the larger are spots that are close together but not as dark.  From the pictures I can find online all three look like the smaller version, this was something I was concerned about when I bought them as I read up on the mistaken identity. 
 
From what I read the juveniles can be mistaken so it is possible I received the wrong species.  Are there any defining elements I would be able to discern if it is the larger species?

 

[ncguppy830]

coloration and size difference