Not dumb question,sure you can do it but why.If you are trying to change water parameters a RO unit will be more effective and less costly in the long run.Most human units use carbon and are costly if using lots of water.
Mrchub
I think you might want to detail your tank size, filtration being used, types of fish and your current water parameters.For some species and breeding purposes it is common to change water parameters.
Most fish will adapt to water conditions.