Possibly the shorter distance from the Amazon to the USA may stress them less, and so they are hardier. The mortality 'en route' and in the dealer's tanks is way to high. And most sold die within a few weeks, the fish either starving or failing to adjust to community life. Otocinclus are not popular here because of their habit of taking mucous from the sides of large fish, especially discus and other cichlids. Although usually said to be because the fish are starving, it may be a natural behaviour.
Green algae is mineral and protein poor.
All loricariids need invertebrates in the diet. Possibly a good alternative is Hypoptoma, a loricariid that reaches a little under ten centimetres. It looks like a giant Otocinclus. But I have no idea about its mortality during collection and import. Common plec species are farmed and 'wild population' friendly.