Hi MC and welcome to fishlore.
Im afraid that your 45 g tank is already pretty much over stocked. Your clown Loaches will grow close to 12 inches each, your Leporinus will grow to about 9 inches each, and no telling how big your Giant Catfish will grow to.
So as you see.. it seems that there are more than enough inhabitants in your tank right now. Your Leporinus will be aggressive towards each other as you are finding out and can be aggressive towards the other fish as well.
IMO I really wouldnt think about adding any more fish to that tank...

~ kate