I have a brittlenose plecostomus in a 25l tank right now and it is only 4" long. I have heard that they grow very big but mine has only grown 2" in about 5months and I don't want to get rid of it. I love bottom dwellers but if it is unhappy then I don't want to keep it. It seems very active and happy at the minute and I am hoping to upgrade to 60l.