Matt - you're making it way to complicated. To get the pH just right, you'd have to know the alkalinity also (buffering capacity). I have a pool also (~18,000 gal - 68,130 L) and when my pH gets to 8.2, I only have to add about 1/3 gal (~1.26 L) of muriatic acid (my HCL is about 10.2 M) to get it back down to about 7.5. I would start by adding about 1.5 L of acid, let pump run at least 24 hr, then check pH. Then add more HCl accordingly to sneak up (or down) on it. Key is to mix (pump) for at least 12-24 hrs before adding more HCl. If you don't mix well enough in between additions of HCl, you could get too acidic and cause other problems. Be patient.
I hope you are still around. I too am VERY interested in this topic - FeO4 or K2FeO5. I have (many years ago) experience with synthesizing perbromate using F2 gas per E. Appleton's method for my masters research project. I did a one-time attempt to make FeO4 using the same method starting with K2FeO4 (ferrate VI) in concentrated KOH. After fluorinating the purple solution for a few minutes, it turned white, fizzed and bubbled for a few minutes, then slowly turned a yellowish-brown. Don't know if I made it, then it decomposed in the caustic solution. Like you have never be in a position to try this again or attempt any other procedure. Please respond if you are around. Thanks.