are important in SW
especially in a reef tank. You can do a wc
either weekly, bi-weekly or monthly. If you do them weekly or bi weekly you can do a 5-10% water change. Monthly I would do 15%. You can do more if you want but I would not do over a 40% wc
unless its really needed.
mix water in a tub for at least 24 hours before using and bring the temp up to match the tank.