When we bought minnows they were bagged and they told use to place bag on tank water for 1/2 hr or so to let them adjust to temp,
I’d think if the timer wasn’t pumping in very much water it wouldn’t shock them.
Friend of mine(brother) has duck club on the river and we catfish run lines in summer, the neighbors traps rice slicks for us and uses an old freezer to keep them in, he’ll run it from time to time in the summer to keep them cool, worked good to good we showed up to fish and the bait was in a big block of ice,
He had gone to town and forgot about them we got him a timer for Christmas ha
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