ph at 7.8 good or bad

it is perfectly fine as long as it is stable
check your ALK, Mg, and Ca though to see if it is

Ph, alkilinity, and calcium levels balance each other. If your pH is low it may represent an imbalance with the other parameters...most likely alkilinity. You state that your reef is a success. That is good, yet if your parameters are off and you correct them your reef may excell farther than its current state.

I highly recommend that you have an alkalinity test and calcium test done. I would also test the pH with a different test kit.

Post back and let us know what your readings are.

Stash low ph is often times caused by too much organic material in your tank. You don't happen to have a crushed coral substrate with large preds do you bro . I'd add buffer and s-l-o-w-l-y raise your ph between 8 and 8.5.
cheers
Max