Mystery Water Parameters

Greetings,

When I originally set up my current 75g planted tank, the tap water
here was pH ~7.0 with a gH of ~2 and a kH of ~1.5.

Now, a year later, the water coming from the tap has a pH of 8.3!
Even though the hardeness levels have remained the same.
(And no, it's not the test kits...)

Aging the water doesn't help, and makes water changes a real PITA!
Am I going to have to resort to RO/DI water?

What on earth are they adding to the water that is causing this?
What could be in the water that it doesn't effect the hardness levels?
Also, water changes are causing algea blooms.

Thanks for any insight,
Greg