I have to agree about the Clown Loach; they are only happy in a group, and as they can grow to over a foot long (30cm) a group of them takes quite a bit of stocking capacity.
Also Angels can grow big enough to eat Neons and Guppies. You don't mention what kind of catfish you have, and some of them grow big too. Also what kind of algae eater; if it was just sold under the name "algae eater" it could well be what is usually called a Sucking Loach. These, like the Red-Tailed Black Shark, grow to 6 or 7 inches (15-18cm) and often become quite territorial with similar species. they might well grow to hate each other, and possibly the CLown Loach as well.
This situation is what I would consider a perfect excuse to get more tanks
If that's not an option you might condsider;
- rehoming either the algae eater and/or the shark
- rehoming the Clown, or getting him some friends once the above are rehoused
- rehoming the Angels, OR replacing the Neons and Guppies with slightly larger shoaling fish, such as the Cherry Barbs, other barbs, or larger tetras
- identifying the catfish to see if it will cause you any trouble later.
The problems will only start when the Angels, Shark and Algae Eater (if it is a Sucking Loach) grow up (and the catfish if it is a large one) so you don't need to rush in to anything yet, but it would be adviseable to plan ahead.
Again the best plan for nuts like me is 'more tanks', but I realise that is not always possible
If you can Id the catfish, or post a pic here, I am sure some-one will be able to advise on that, you could also Google Sucking Loach and confirm whether or not that is what you have as an algae eater.
hth.