There is some considerable confusion in this thread.

Firstly, regarding gizmos question:

The two mose likely reasons for your pH rising:
1) you may use water supersaturated with CO2 (water from wells often
is). As the CO2 is released into the atmosphere, pH rises.
2) you have some limestone in your tank, perhaps in the gravel, or
perhaps you have seashells in there? I think this is probably the
reason for your pH rise, as limestone tends to rais pH to about 7.5.
Theoretically limestone can raise pH all the way to 8.3, but the
reaction becomes slower the closer to 8.3 you get, so in practice the
endpoint is, roughly, 7.5. If you want to go higher than that, you can
use bicarbonate to get up to 8.3.

Over to some of the other issues here...

* KH in an aquaristic context is usually the same as alkalinity. This
because most test kits function by acid titration, so what's actually
measured is alkalinity. If you add phosphate buffer to an aquarium,
that will add to the alkalinity, it will add to the reading you get
from a KH test kit.

* A quoted message stated that to measure the effect of acidic buffers
such as phosphate buffer one'd need to titrate with base instead of
acid. That is only partly true. A buffer resists all pH movement, up
as well as down, and phosphate buffer will add to the alkalinity
measurement also when doing an acid titration provided the endpoint is
below the set pH for the buffer (i.e. phosphate buffer will show up on
a KH test).