10% every 8 days (due to shift work). I run Balling light on my tank so 10% weekly is recommended to maintain salinity and avoid a build up of chlorides.
I think basing water changes around test results is a poor choice as there is a lot of elements required by your tank that are not tested...
Certainly not advisable if you running something like balling light on your system.
A 10% weekly water change is a neccassity to avoid the build of chlorides and over shooting your salnity.
How do you go about replenishing essential trace elements required by your corals?
Tottally disagree with this statement.
External filters can be used quite happliy on a reef tank if they are cleaned on a weekly basis and not used to run media like sponges/bio balls/ceramic rings.
You can happliy run an external that contains phos remover (although this is much better...
Behind the tank (UV and Po4 reactor):
ATI Sunpower and Aquamedic Turboflotor Multi SL:
Close ups:
Vortech MP40ews controller:
Tunze Auto top up controller:
ATC 300 temp contoller: