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[Scavenger]

Dale, one thing you might be able to do to make your intertidal critters feel more at home is add some form of chilling to the sump but not the display tank.

That way, as the tide is dropping the ambient temp of garage might warm display water a bit, like a true tidal zone.

In the sump, you could even try to figure out your evap rate and have an ice cube dump for your top off if you can't afford a chiller.

Once the return kicks in (raising tide) the critters will be hit with colder water much like the natural enviroment.
Just a theory, but I'd guess certain behaviors in your livestock would be more triggered by temp than light.