Do you know what the pH was when you first set it up?
It's unlikely since you haven't added ammonia but one possibility nobody has tossed out there is that the pH has dropped over time.
The questions about why you want it at 8 are very valid.
As PNW said, bringing it up to 8 during a ammonia-aided cycle, using baking soda, is really helpful.
But after the cycle, it's possible you need nothing.
There are people here who are far more experienced than I am with the science, but I have a lot of practice at making pH come up from 6. I got lots of different advice from fish experts and chemistry experts and what finally worked was this:
Don't use proper pH, acid buffers, or alkaline buffers.
Test KH and GH. You want them to be no lower than 3-4 degrees, for most tropical fish. Put crudely, GH is overall mineral content and KH is the ability to prevent pH swings.
People who have really high KH and pH, get fish that can deal with it or use RODI water.
If your water has low KH, your pH might go up and down a lot (much more problematic than being consistently low. You can use cichlid buffer (API Buffer Max for cichlid) at a dose to bring it up to 3-4 degrees (50-60ppm) KH.
If you have low GH, use API African cichlid salts or seachem equilibrium to bring that up. GH doesn't affect pH but it is important. Living things need minerals.
GH and KH of about 4 degrees is fine for most beginner tropical fish.
If you're keeping cichlids that need high KH and GH and pH, the cichlid salts and cichlid buffer are a natural choice.
The proper pH products, I've found, just make pH go up and down a lot.
If your KH and GH and pH are good from the tap, frequent large water changes should be adequate.
My LFS also saved me from a lot of pH stress having me use a wide range pH test that isn't more specific than 6, 6.5, 7, 8 ... It's one for hydroponics. They said even their store, which sells sensitive species, uses this test, because sweating over .2 increments is nonsense.
Sent from my iPhone with three hands tied behind my back.