PH increase to 8.5??? Why?

[y-not]

Here's the scoop on the basic hardware:

RedSea Max 250L (66 gallon).
Stock Skimmer.
Stock pumps.
BRS charcoal reactor.
Two Hydora 750 circulation pumps. One on the left. One on the right. Both blowing towards each other but they are separated by about 60 pounds of rock.
The tank is 18 months old.
I've been using the same salt mix for the past year. Still mixing from the same bucket for the past month. I change 10 gallons of water every 7 to 10 days.

Nothing new has been added in the past few months.

The issue is that my Apex, API, Hanna Checker and hand held spot checker are all showing my PH is peaking at or near 8.5. It drops down to 8.2/8.15.

Up until two weeks ago, it seldom peaked to 8.2. The low side was 7.8.

All other parameters are perfect.
I've got two, very happy clams that are showing the typical white edges of growth. Most of my corals are doing well. Nothing seems to be suffering.

What would cause the PH to creep up like that if I'm not adding any additives and using the same salt (very same bucket for that matter) as I have for a few months?

 

[mikesmith34]

A change in the weather my brother? AC not coming on as much?? Not sure it's high enough to be worried about but interesting question.

 

[y-not]

Mikesmith34;987056 wrote: A change in the weather my brother? AC not coming on as much?? Not sure it's high enough to be worried about but interesting question.

Nope, not worried. Just curious.
It didn't jump up like this last year. Just wondering why I would have seldom seen it make it to 8.2 then seemingly out of nowhere, it's topping out near 8.5 and bottoming out at 8.2.

 

[y-not]

And...for what its worth, I'm not a PH chaser.
Just monitoring my parameters and for some reason, the PH jumped up higher than I've ever seen it.

About 6 months ago, I toyed with dosing Kalk.
It would get up to 8.4 but only when the ATO was topping off and I could tell by the tiny peaks on my Apex graph, when the ATO was topping off. That was sort of cool but...my calcium was starting to get to the 500 level so I quit using the kalk after about a month. Since then, my water changes have kept my calcium and mag at the perfect levels without dosing anything.

 

[marquiseo]

An empty home can do that. Not many people in the house to produce CO2. Leaving the window up/door open can do the same because you are exchanging air for CO2 bringing down the levels which raises your pH in your tank. It will do that mostly during the summer time and less during the winter because little air exchange is being done to your home because of the cold. (You wouldn't open your windows in the winter)

 

[y-not]

Yeah, maybe but again, nothing new our different has been happening around our house

 

[marquiseo]

Y-Not;987069 wrote: Yeah, maybe but again, nothing new our different has been happening around our house

I wouldn't worry about it. If it gets dangerously high, then retrace every piece of equipment in your tank.