low Ph?

My Ph seems to hover around 8ish. All other tests. Are perfect (amm @0, nitrites @0, nitrate hovers around 5ish), Thoughts?



40 gal, 2 clowns, 1 cardinal, small slug, small cuc, Emperor 400 with matrix in secondary, Coralife super 65 skimmer, sand bed (although admittedly not very deep.), not sure rock weight.