I have had a conch in my 29 gallon for a few months, I'm not saying I know it will last forever but it seems to be doing great so far. I added it after 7 or so months and it is my only inhabitant that really cleans my sand. I'm not sure how big it will get but I really enjoy having it. My sand bead is a little over 2" and he is no where near running out of food.