I can add a comment that may or may not be helpful. I use sodium percarbonate to kill algae in my Koi pond. It almost always leaves behind a lot of calcium carbonate precipitate at the bottom of the pond, which is sort of a problem, but managable. It does, of course, produce a lot of hydrogen peroxide at low cost. I am not recommending this, but it may, and I say may, be possible to put a little of the percarbonate into a plastic pail with water and then let it sit for a bit of time to let the calcium carbonate settle to the bottom of the pail. Maybe enough calcium carbonate will settle out that you can still use the hydrogen peroxide that is still in solution without disturbing the precipitated calcium carbonate. You will likely still get a big rise in pH and alkalinity, but likely not as much as would be the case of just putting the percarbonate directly into the pool. Again, this is just a thought, and I would encourge you to exercise caution in whatever you do. Getting rid of fine, precipitated calcium carbonate once in the pool it not an easy task. Good luck.