Should I be worried about my fish?

I have a 40 gal tank. With a bunch of peaceful community fish, and 2 albino bristlenose plecos. I got them at the same time, put them in the same time. But one of them is almost tripled in size and the other one barely grow 3 millimeters! Should I be worried about the small one? I don't have any food for them, they just rat all the algea and stuff. Why is the other one so big and the little one isn't? Is it dominance? If there is, is there anyway I can stop it? The only orther tanks I have is a 10 gal anda 5 gal with I wouldn't trust the water, and. A20 gal with 2 already in it. Which those only have a little bit of a size difference? Y r those the same size and not the ones in the bigger 40 gal? Both tanks have live plants and 1 piece of drift wood per tank, with plenty of cover! I also have a question about snails, in my 20 gal, it has the most plants and about 3 days ago, I found a little snail! That's a bad thing cuz last time I have snails, the laid eggs everywhere and I didn't have the heart to kill them when I cleaned the tank or what ever, unless it isn't a bad thing if the snail doesn't eat my plants or have babies, the snail is small brownish, it's shell is kindof see through, I would explain more about it but I can't even find it.. It likes to "hide" cuz I never can find it. And I don't no how to link a picture to a website or watever so u can see it,. Can u name and or attach links so I can see all the snails that the store (petco) might have and the ones that are harmful to a planted aquarium and eat plants!??!? Thanksss actually I found the snail, it has a half of a football shaped body with a pointed tail, it's brown and small like I said. Sorry I didn't feel like erasing wat I wrote when I said I couldn't fins it but plz answer any questions that I wrote! P.s ik this is alot but sorry and no mean comments