Also, read up on their dietary habits. Improper feeding is one the major causes of loss in these fish. Here is what this sites states about feeding:
These fish are grazers, but not in the sense that they eat only vegetation. They actually sift and chew at the film of organic matter on hard surfaces in search of higher protein foods. In the wild this would constitute mainly of algae and vegetable matter, but with a variety of foods from small insect larvae and crustaceans to other animals eggs. With this in mind, a largely vegetarian diet, cucumber and courgette appear on the accepted menu, with treats of frozen foods such as bloodworm and blackworm, along with frozen prawns. Algae and plants are avoided. Accepted food morsel size changes with age in all of these fish. Best results are obtained by offer these foods in a paste. The very long intestine of these fishes indicates a biology adapted to breaking down food high in vegetable content.
The one thing the above doesn't stress enough (imo) that these guys pretty much feed on and off all day long. They do not do well if you try to feed them a single meal every day. You might want to consider feeding Repashy brand foods. A few advantages of this are you can mix different types such as the veggie and the meat food to create a blend. You can also "paint" this food onto rocks before it gels and then put these into the tank.
Here is what is in the "Back to Nature Guide to L Catfishes" by Ingo Seidel:
Diet: Highly specialized Auwfuchs- feeders that should be fed on an almost exclusively vegetarian diet of food tablets and a variety of vegetables in the aquarium. It is essential to avoid too much animal food - which is eaten readily. many aquarium plants will be regarded as food.
Maintenance in the aquarium: Not recommended for the beginner. Only under truly optimal conditions (high water temperatures, frequent water changes, feeding several times per day) are the juveniles usually imported likely to achieve any meaningful growth. Adult specimens are, unfortunately, frequently territorial.
from page 79.
but anyways, i have just bought a 160 litre tropical aqaurium to have a community tank as my old one is too small and i wanted to upgrade, one of my favourite fish is a golden nugget pleco but i do not want to buy one for over 30 pounds and then my something fatal happen to it so i was wondering if anyone knows maybey how long i should keep my tank running for before i consider the idea of putting a golden nugget pleco in there, thanks 
