I ahve always had good luck feeding very meaty foods to heliofungia. Mysis, krill, Rod's food, etc., and lower flow generally gets them to have the super long tentacles. I had one for years (sold him in a move) that I kept in higher flow than my other helios, and his tentacles never extended as long, but he was perfectly healthy. I moved him once to test into lower flow, and sure enough got another 2" of tentacle extension.