Clown loaches were my most "veggie-rific" fish I think I've ever kept
Beyond barbs or plecos nibblng a few. I always felt those last fish would have preferred algae straight up!
Have you offered your clowns zucchini with a food pellet they like stuck in it? Whee! Mine caught onto that fun food pretty fast! I think sometimes our fish eat out of boredom; I'm pretty sure my clowns liked punching holes in romaine, swords or crypts whether they actually ate them or not.
Have you seen the goldfish soccer games, etc. videos? Our fish can get bored when they don't have to work hard for food.
I don't remember festivum eating plants but that may have been before we knew some fish liked veggies...live & learn. We just didn't know back then...we do now!