If you have a refractometer, shoot for 35 ppt
. That is going to be the best level for maintaining most invertebrates you will end up keeping.
How are you storing the refractometer and do you clean it after each use with RO
water and a soft clothe? The lense and cover should be wiped clean to prevent salt build up after each use. Somethings amiss if you need to recalibrate it before each use.
As far as your water changes are concerned, do enough to keep the NH3
below the 0.5 mark. The already established bacteria just needs time to multiply from your previous cycle. It should quickly subside but in the meantime, the water changes will help the survival rate of your hitchikers.