It is low for that time of day. I would not suggest adding buffer until you know the cause. The buffer is just a bandaid for an underlying problem.
More often than not, poor ph
is due to lack of surface aggitation, insufficient gas exchange from a covered tank or high ambient CO2
in the tank room. If the alkalinity of the water is good and the ph
is low, that would be the best place to start.
What time do the light come on in the morning?
Your profile also says you are just converting to saltwater. If this is a cycling tank, the ph
will do wonky things for now and should not concern you.