"Glenda" wrote in
link.net:

James, you don't mention what the specific gravity (salinity) is.
This could be a factor, but your KH should balance it out as your
amonia goes down. Also the time of day that the sample was taken will
have an effect on the ph. You will notice slight variances between
morning and evening samples.

Salt concentrations do not affect pH.

pH fluctuations during the day are generally dependant on living organisms
respirating and photosynthesizing within the aquarium. It is the
production and use of CO2 (carbonic acid) that is the main culprit for
these fluctuations during the day--in a cycling tank there isn't likely to
be a lot of that going on, however it is wise to get into the habit of
testing your pH at around the same time each day anyway.