Thanks for sharing those videos, very helpful!
Your TA test looks correct. (to speed things up, I just keep the spinning/mixing going the entire time I add in my drops, rather than stopping it each time. You can STILL see the color change if you leave the spinning/mixing on the entire time).
You pH test looks correct as well .
Note on BOTH tests. Try to hold your bottles completely up/down (vertical) when the drops are coming out, instead of partially sideways.
Thanks for sharing those, now we know your testing is good. Now that you've validated your tested with the video, you can ignore the strips as well. (again, I suggested only as a cross-check until testing was validated)
At this point I'd concur, you just have to keep adding in the MA until you see that pH come down. For now, I would recommend targeting NO LOWER than 7.4 or 7.6 on the pH, however, because you don't necessarily want your TA to drop too low either (you're at 80 now which is okay). Your pH *HAS* to come down eventually. If you were previously running your waterfalls constantly, it's possibly your pH rose up to levels that we normally don't ever see (and believe me, I know how much waterfalls aerate and raise pH because I have 6 water features in my pool that create massive aeration).