Oh that's easy. Timers, float switches and pumps LOL
One pump to pump out the old water, another one activated by a float switch inside your tank to pump water in from a makeup bucket. For your makeup water you would need a bucket, a motorized unit to dump salt in once the bucket is empty and another float switch to add water to the bucket after the salt was dumped in. Finally a timer to turn on the powerhead and heater.
Easy as pie LOL
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230 mixed reef / 230 gal sump/fuge
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