You're using the term 'filter feed' totally incorrectly.
Wood shrimp filter feed.
Basking sharks filter feed.
Baleen whales filter feed.
Flamingos filter feed.
Sponges filter feed.
All involve taking in water and passing it over a filter, which collects the food for swallowing.
Corydoras do not possess such a filter.
Corydoras do not 'filter feed'.
They may take in food-laden sand, but their mechanism for extracting that food is not a filter.
Go tell that to the authorities, and see how far you get.