will brackish water kill the ich on my mollies?

Since they are BW fish anyway, it might help. Also, raise the temp to 86.
 
1-3 teaspoons uniodized salt per gallon of water will work. Continue with the salt for atleast 1 week after symptoms are gone. Rock salt or aquarium salt. Some people say normal table salt is fine, but some say not. I wouldn't use it. Make sure it's fully dissolved before putting it in the aquarium.

This doesn't actually make "brakish," as brakish water has more than just salt in it.
 
I agree,
best way to do is raise temperature to 86 and slowly raise salinity levels,
mollies are best kept in brackish waters
but dont use table salt, it's totally different to sea salt.
 
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