My experience with any type of water exchange is a 24/7 drip that consistantly administer's the new water. If I were in your shoes I would build a holding tank that could gravity feed a trickle into my pond for maintenance.
What i would do is get a 5 gallon bucket and test the PH out of the spicket. Then 24 hrs later I would test it again. ( I suspect it may furthur soften)
then I would add the acid of choice to that 5 gallon bucket and see what % of acid it takes to bring down the PH to where you want it. I would apply that % to my holding tank that I intend to create my drip from.
I think Larry's advice is very sage, nothing like a club member who's been there done that to give you the best information going. all the best.....
