Good rule of thumb is all plecos are more sensitive at smaller sizes. That said, I don't find them too difficult. Plenty of flow, warm water, and a good varied diet is the trick for any of them. Just curious what you're paying for a little guy like that?
3" is a safe size to buy a Pseudacanthicus. As stated above good water conditions and correct temperature is important. For that size 83-84F is the sweet spot. Colder they don't eat well and seem to get sick easier. Over 85F increases their metabolism and stresses them long term. The larger the more indestructible they are.
Prices are a little higher this time of year