First off, please forget clown loaches (Chromobotia macracanthus). They must have a group (all loaches are highly social fish and this is critical to their health) and this species gets very large, between 8 and 12 inches is normal in an aquarium, but it has been reported to reach 16 inches. It requires at least a 6-foot tank.
In a 4-foot 55g, the YoYo Loach (Botia almorhae) is a better choice, and a group of at least five, but six or seven would be better, will work. This species is generally peaceful, but all loaches are "playful" to varying degrees [observing the so-called "loach dance" is fascinating] and many can fin nip upper fish, especially long-finned species; rainbowfish (the larger species you have been considering in the other thread) should be active enough to be safe, but I can't guarantee it.
Another loach that is perhaps the most docile of all of them, though still a playful fish, is Botia kubotai. It also reaches around 5-6 inches (like the YoYo) and obviously needs a similarly-sized group. I have not observed any problems from my shoal that I have had for 4+ years now. Any of these Botia species will be fine in your soft water.
These will eat snails, to some degree, but here again I am puzzled why you would consider snails an issue? They are extremely useful inhabitants of a fish tank. I have hundreds in my tanks, and while they are fewer in the two tanks with loaches, they still manage to hang on fortunately.
A word of caution with corys...I personally would not combine corys with loaches. Loaches are territorial, some very much so, and other fish bumbling their way into the loaches' space may not be welcomed. I'm sure some will say they have these together, but it is something I would never consider. And corys and loaches are not going to "chum together," so to speak, as the corys and loaches will need to do with their own species. There are very few species that mix together in a way that approaches the interaction within a group of the species; this is an inherent need of the particular species.
As you can see from the above, when one begins considering this or that fish to deal with an issue, it is possible to introduce even more issues that may have consequences. Adding fish is never the way to solve an issue, unless the fish will fit into that particular environment and be a contributing part of the whole.
Byron.