I have a fish that might be sick

[Blue Ring Octopus]

So I want to put him a hospital/observation tank, brand new water, heater and sponge filter, does the fish have to acclimate to the new fresh water. Kind like a kid from Los Angeles going to Yellowstone and taking a deep breath.
Thanks in advance

 

[Rocks reef]

Are you going to use the same salt mix for your QT tank? As long as the salinity and temp are the same, you are good to go.

 

[Blue Ring Octopus]

Yes it is the salt mix that I have been using for a year now.
I will transition later after everything gets back to normal. Start with 25/75, 50/50 75/25.

 

[Rocks reef]

May I ask what the ratios are for?