HyperCube33 wrote:
What conditions prompt a water change? What test kit results (high nitrates,
etc) would be an indication for a partial water change?
Debris buildup...blah blah.

Any favorite tools used to change the water?

Hyper....
The conditions that prompt a water change a
Being that it's a tank and not open water which is constantly refreshed
naturally.
Ammonia readings...if it's not zero, water changes are needed. (new
tank syndrome, etc.)
High nitrite readings. (new tank syndrome).
High nitrate readings. (old tank syndrome).
Over feeding.
Before or after medicating.
New fish added (after quarantine period).
Probably some I have forgotten too, hehe.
Now you asked about what test kit results would indicate a water
change. That of course would depend on the individual kit, as they are
different and have different numbers. It would make it so much easier
if there was one standerd test for each, but there a several brands and
even different types from the same manufactor.
So that was a bit of a loaded question and one that cannot be answered
without a specific test kit in mind.