0.4 pH swing...bad?

[Son Of Skyline]

With my new Pinpoint pH monitor, I've just learned that my tank swings from 8.08 before the lights turn on to 8.51 when the lights go out. Is this daily pH swing stressing my animals and corals? I know they haven't looked the greatest lately, but nothing has died, everybody's eating and my corals are still growing...slowly.

I drip kalk when the lights are out at about 2 drops per second. The drip stops when the lights turn on.

What's an average pH swing in a healthy tank? Thanks in advance