Scott,

Just do a couple of large water changes, that will remove the PO4
buffer.

Now........the algae etc, these are CO2 issues.
If you want a specific pH, use CO2 to do that, otherwise, do not add
any buffer other than baking soda to get the KH to about 3 or so, most
all brands are fine.
If the tap is 3 degrees or higher, you don't need to add any baking
soda.

PO4 of 1-2ppm is ideal for CO2 enriched plant tanks.

Regards,
Tom Barr