so if it were me i would do say 25% or alittle better on the water change not too much or it will shock everything change the carbon asap and regen the chemipure and maybe another water change say mid week also maybe stir the sand alitte when you do the change but not to much as it could be storing bad things and possibly leaching into the water hope this helps let me know if there is anything i can do to help.
kevin

hey just did the water test i only tested the main things
salinity 1.028 not bad 1.025 is normal
phosphate 0.0-1.0 bad should be 0
high range ph 8.0-8.2 good
nitrate 10 bad
ammonia 0.50 bad
magnesium 1160-1200
should be 1270 at 1.025 salinity still not bad