Yoyo Loaches/Pakistani Loaches/Botia Lohacata (sp) now Botia Almorrhae (sp) as i really cba to look up spellings lol have so many names...
Get to about 15cm and once that size, can be little devils, not all are but i have seen them decimate guppy populations and shred fins faily regularly.
Tizer was spot on with Botia Striata, the Zebra Loach. They are brilliant! 8-10cm and you could fit a few more in and have even happier loaches! Plus they are so gentle! I found they shoaled with my cories sometimes lol.
EDIT: Clown Loaches dont necessarily grow when kept in a tank big enough, the biggest one will be the dominant fish, the more dominant the fish, the faster they seem to grow.
But if at 5 years + (depends how old it was when you got it!) and only 4", you know its not in a big enough tank... it isnt just 'some' clown loaches that get big, its just... only some are kept in appropriate size tanks and are given a chance to thrive, get to the size they are meant to and live as long as they are meant to.
I always get asked "don't clown loaches only grow to the size of the tank?" at work and my answer is always the same... they grow as big as they can and then they end up dying. Whether from the water or stress related or something else... might take a year... might take 10 but they wont live as long as they should in a small tank and therefore its just going to kill them.
I love clown loaches, one of my favourite fish but i wish they would ban importing them so they didnt all have to suffer. Had a customer who i refused to sell clown loach to so she went to a certain other large pet supermarket and bought 3 clown loaches..... for r baby biorb. *sigh*