We in the middle of Europe most effectively deal with Hydra by using Flubenole. This is a white powder not to be bought in pet shops but in pharmacies or with veterinarians only. It is put on the water surface in very small quantities (“a knife’s pit”), and even if there is no circulation it will definitely destroy Hydra within 36 hours. You can observe them contracting within the first half of this time and they disappear without leaving any of them left within the second. The substance is without any harm to fish, but may affect snails. But snails should not be kept in Parosphromenus breeding tanks.
Licorice gouramis will never eat Hydra. In community tanks one can have a try with Colisa or Trichogaster, but that will work only if the fish are really hungry and have no feeding alternatives. In a planted tank they will never get all Hydra cleaned.
In my view there is no alternative to Flubenole. It’s harmless and very effective indeed.