1.024 may or may not be correct depending on what you use to measure your sg
. If it's a floating hydrometer or swing arm hydrometer I'd lower it to 1.020 (assuming it's not reef) to give yourself some room for error. If you use a refractometer then I'd keep it where it's at.
Main thing is if you remove SW
you replace with SW
and you top off evaporation with FW
to maintain the sg
since salt doesn't evaporate. Adding 4+ gal
would lower your sg
You can use a lower sg
mixture to lower your sg
in the main. For 20% I'd recommend an sg
of 1.018 which will lower your mains sg
to around 1.022-1.023. After doing this a couple of times you will get your sg
reading to 1.020.
Also FWIW fish can adjust to lower sg
/ph much quicker than trying to adjust to a higher sg
/ph. If you have inverts adjusting sg
/ph should be done very slowly. To increase slowly (if needed) topping of your evaporation with SW
is the easiest way IME.
Mix your SW
with a ph for 24+ hours and match the temp/sg
/ph to the main (unless trying to lower/increase in which case it should only be off slightly)
If your SW
isn't properly mixed it can be caustic to fish/inverts and shock or kill them.