I don't do anything different for my Malawians and Tangs. But, I live in Iowa and because of the South Dakota aquifer our water is very hard. Can't keep apistos that is for sure...without R/O.
All I would do would be take the other fish out and do a water change...a big one 40% or so then move them when the temp is the same as the tank they are in.
You don't mention pH or kH for the tank(s). Do you use Tang or Malawi salts for each respective tank?? If so, just remove the Malawians do a water change then use the other salt. Shouldn't be that big a deal to get this done though.
All I would do would be take the other fish out and do a water change...a big one 40% or so then move them when the temp is the same as the tank they are in.
You don't mention pH or kH for the tank(s). Do you use Tang or Malawi salts for each respective tank?? If so, just remove the Malawians do a water change then use the other salt. Shouldn't be that big a deal to get this done though.