What are you using to test your Ph? Check your test kits if that's the
method you are using. You know Ph swings of a few tenth of a point are no
problem. But it's the drop that's in question. Do you use a Ph probe? Have
you recently calibrated it? The harder (and longer it takes) to calibrate it
can mean a bad probe. I've been there before. - check the pin-point monitor
& seeing it read 7.8 & you know it's goofy!
Also, I've heard that ppl back east seem to have CO2 build-up in their
homes causing tank Ph's to drop during the winter, I know it's summer but
it's just a thought.
Steve

wrote in message
...
I have noticed my PH going down from the normal 8.2 at 10AM to
8.4 around 11PM for the past 4 years. But over the past year
my readings have slowly gone down to 8.0 at 10am to 8.2 at 10PM
over the last 6 months its more like 7.8 at 10am to 8.0 at 10PM. I
recently did a 200 Gallon water change and the readings went pack up
to normal, 8.2 -8.4 but within a week or so it is coming back down
again to the 8.0 - 8.2 range.

I am using Tropic Marian salt which I thought had the best buffer
capacity but wondering if that is my problem.

Does the 500 pounds of sand in the tank have anything to do with the
buffer capability of the water? I did not think so, but wondering if
that gets depleted.

Of course Alk, KH go down as the PH goes down, if I boost ALK the ph
goes up it is just a temporary fix.

Any thoughts or comments would be appreciated.

Thanks
James