Why I Can't Buy Pool Chemicals On Saturday

I went to the local pool-supply store this weekend to buy chemicals for our hot tub, and, unlike two years ago, it was closed, and only open on weekdays.
I went back on Wednesday and asked why they were closed. The owner replied, “When everybody and their uncle started selling chemicals, it didn’t pay us to be open on weekends anymore.”
Most of their pool- and spa-servicing business is on weekdays. But until recently the store could still cover the variable cost of remaining open on weekends, because customers, most of whom work and couldn’t come by during weekdays, would buy pool supplies on Saturdays. With the competition from Home Depot and others, the store can’t cover the variable costs of remaining open on Saturdays, so it closes. The firm shuts down in the very short run, but it remains open on weekdays, when there is enough business to cover variable costs; and, as my purchases show, they also sell a few chemicals then too.
This would seem to be a fairly common response of small businesses when larger retailers begin to offer a non-specialized competing good.