I run low alk (6-6.7 dKh) simply because it ended up there a long time ago and I chose to focus on just keeping it stable, rather than raising it.
I’ve also had pretty good success with SPS at those levels. I don’t think that has anything to do with it being low, there’s just no incentive to change it.
Some pictures to support my anecdotal account: 7 months growth from June ‘19 to January ‘20. The little Walt Disney from the first picture is sitting on the rack in the second pic. Cut a frag from it and put the frag in its old spot.