Thank you so much. I'll do the test tomorrow and post an update.if this is true then it is as Randy stated can only be co2 in the water and more than likely the room. Depending on size of tank and co2 levels in the room it could take 24 hours or longer with windows open to see a significant rise in tank ph. If the levels of co2 are elevated enough then the exchange at the water surface of the tank and sump may exceed what your skimmer with co2 scrubber may be capable of doing. Do Randy's test with water sample outside. Obviously you will need a different ph meter as your Apex is not going outside. Be sure what ever meter you are using use it to test the tank and outside. There are many articles on reef2reef on raising tank ph and if you really need to.
I foresee is co2, the big problem is going to be how to fix it.
If I try to run a pvc line outside is going to be 30ft long, cause of the house layout. And not sure if such a long pipe will deliver fresh air to the sump area...