Flag fish feeding

My flag fish has an overwhelming preference for stringy shaped foods. I tried zuchini and peas and algae wafers, he has almost no interest in those. He gets most of his veggies from eating roots, mostly of floating plants and also from some of the rooted plants. He will also bite of the tips of tenellus. It has to be long and thin and string shaped or he doesn't want it. He'll eat duckweed leaves, but mostly he likes the roots. I'm starting to think that the reason my red root floater is dyeing out is because the flag fish is eating the roots.

The stuff from the asian market would probably work as long as it didn't have a bunch of salt or MSG added to it or something.
Pumpkin is a good flag fish food. I used to save the jackolantern pieces and the guts, cut up, boil, freeze in ice cube trays, and feed them to my plecos, snails, and goldfish but the 2 american flags would get in on it too. They would chase the pieces around the tank in the current.

I'll only buy the good stuff, no msg or anything, but as long as it won't harm them and it's just a question of whether they like that, it seems worth a go. If pumpkin works, maybe other squashes too...