Have your fish lost their appetite? Have you checked if your heaters are working?
Loss of appetite from incorrect water temperatures are an easy fix.
Tropical fishes like Bettas (see also
https://thefishvet.com/2011/06/05/fighting-fish-over-wintering/) need tropical conditions year round.
If water temperature is not the problem, get TheFishVet out to investigate. It could be a serious disease that could spread.
Dr Richmond Loh
DipProjMgt, BSc, BVMS, MPhil (Pathology), MANZCVS (Aquatics& Pathobiology), CertAqV, NATA Signatory.
THE FISH VET, Perth, Western Australia, AUSTRALIA.
Mobile Aquatic Veterinary Medical & Diagnostic Services.
Ph: +61 (0)421 822 383