why's my pH so low??

[fishface]

hey all!
my pH numbers seem to still be on the low side but can someone tell me if they are still acceptable?

Ca-490 ppm (no supplimentation)
KH-9.3
SG-1.025 (too high?)
pH morning-7.8 evening 8.0
no3 and po4 barely perceptible
added another power head for surface circulation

been using ro/di water for changes (25% monthly) and top off, and raising alk with baking soda but just picked up some kents coral builder last night (better?). anything else i should be taking in consideration or does all seem fine?

as always...appreciate your input...
darryl