The problem with bristlenoses is that they are massive poop machines. I do actually keep a bristlenose in a 60 ltr tank, but it is a female (smaller than males), in an established tank with extra filtration, other tank mates very small and not very many- and frankly, it's not an ideal solution. A better idea would be to up the number of black skirt tetras (if you already have those) to at least 6.
Are there any smal, Pleco that aren't poop machines