These snails have an operculum making them quite difficult for loaches to eat, adding stock is never the right choice.
I submit the idea of some Congo Tetras to consider as well. Perhaps rainbow fish would be compatible for your tank too, but I am frankly unsure on their
I would add an air pump and air stone with a sponge filter. The powerhead you mentioned sounds great for your tank! Good luck!
I like the name of this snail, Assasin snail! Cool! Since there's so many, I would try an assasin snail or maybe a loach (clown loach maybe) that
Do you have sexable ancistrus? Where are you located?