ph problem

Hi all,

I have a 20 gal. fish only tank with crushed coral substrate. My ph runs
consistently at 7.8. What is the best way to raise it up slowly so that my
fish won't go into shock. I'm not crazy about chemicals, but would be
willing to try it if it's the only way. It was my understanding that the
salt mix (Instant Ocean) was supposed to automatically adjust the ph. I
change about 5 gallons of water per week. I have a pair of clarkii clowns,
a yellow clown goby, a 6 lined wrasse, 2 pyramid snails and would like to
add a royal gramma to complete the tank. Thanks,

Sarah