10% water change...tank volume or tank and sump...?

[scattered]

These numbers are all rough approximations/generalizations..
Don't waste brain power overthinking..

Some do 10% a week.. Some 20%.. Some 20% a month.. Some 20% every 6 months.. Some haven't done a water change in years..
There is no "right" answer but to adjust/adapt based on knows we can see/measure,etc... each tank is different.

You forgot idiots like me who change a small percentage every couple days or even do daily automated changes LOL

As a generality: smaller incremental water changes are better for stability; larger less frequent wc are better for dilution.

 

[skipm]

IMO people are getting a little too worried with percentages here. You want to change enough water, often enough to maintain your tanks desired parameters. As an example if you change 10 gallons every other week and you nitrates, calcium, magnesium, iodine, etc. levels are within desired levels then your doing enough. However if your levels get way out of kilter and your trying to do water changes to get everything back in check then you need bigger and more frequent changes. Before you do any changes remember to top up your tank to the proper salinity, salt doesn't evaporate and your salinity levels will go up otherwise.