Water changes

[sharper]

If i do a 50 Percent water change on a 50 gallon tank do i need to replace 25 gallons worth of salt?

 

[rottbo]

yes..... but you should always premix saltwater before adding it to the aquarium

 

[davo]

and check the salinity once youve put it in.

 

[sharper]

if i remove the fish do i still need to premix the saltwater?

 

[Max]

Yes, always premix the salt at as close to the same temp as your tank as possible. I use a large plastic garbage can with heater and submersible power head. That way it's easy to add either more salt or water until you get it right.
hth
Max
P.S. also make sure that your ph is as close as possible.