Tiger barbs?
When you say something is eating your fish, do you mean that you find dead fish with bits missing from their bodies or that you've seen live fish with bits missing that later died?
If it's the first case, it is most likely that the fish have died and then been eaten. The vast majority of fish will eat dead ones. So you need to ask why are your fish dying rather than what's eating them. What are your ammonia, nitrite and nitrate levels? If you don't have your own test kit, take a sample of water to a fish shop that does testing, but get them to write down the actual numbers.
For fish live fish that have bits missing then die, I would suspect the tiger barbs (if that's what they are) or just possibly the black widow tetra. Both of these have reputations for nipping, though it's normally just fins not the body. These fish are particularly nippy if there aren't enough of the same species, enough being a minimum of 6, preferably more. I do realise you've had fish die which will have reduced their numbers, so I'm not critising you for not having enough, just that it's something to be aware of.
Can I ask, what size tank do you have? Either the volume or the measurements. I'm asking as you have clown loaches which need huge tanks - they grow very quickly in the first few months, reaching over a foot/30cm long eventually. If they are in a small tank, they could become stressed and stressed fish get sick easily.
And what fish have died so far, how long after you got the tank? Also did you do a fishless cycle? Fish that are subjected to high levels of ammonia and/or nitrite during a fish-in cycle can die well before they would normally.
If you can give as much info as you can, we'll be more able to get to the bottom of it.