Cow was the last to die Saturday morning. Perimeters are all perfect. Salinity dead on. I will have to see if I can find Ruby and anything is worth a try. The pictures as well as detail was in a previous thread.Makes sense with mucus separating from FW dip. Realize this step only provided Temporary relief. Im aware of canada issue with meds making it difficult. Other than Formalin, are you able to get a hold of ruby rally reef pro? This will take longer but work.
Another although not the actual treatment would be PraziPro. Note that prazi will reduce both appetite and oxygen.
You can increase oxygen with an airstone now which may be part of their distress right now. ASSURE ALSO THAT AMMONIA LEVEL IS NOT HIGH (above .03)
Lastly, do note also that as cute as they are, COWFISH is very difficult to keep in captivity and rarely are long lived in an aquarium. When they perish, they can release toxins that may have caused the death of the other two fish. Adding chemipure blue will prevent effects of toxins in your tank and improve water quality. Lights out will likely do nothing for the fish but you can