Congratulations on winning your battle!

So it does seem that the rule of maintaining a minimum FC of 15% of the CYA level (so 10.5 ppm FC or around 11 ppm FC at your 70 ppm CYA) does seem to work for yellow/mustard algae. This is double the rough minimum FC of 7.5% of the CYA level for green algae (corresponding to the "Min" column in Ben's chart).

Some other users had success using PolyQuat 60, but had to maintain a weekly maintenance dose of it -- not a one-time treatment. It apparently helps slow-down growth, but does not kill all the algae, and may also need at least some chlorine level as well. Did you do a one-time dose or did you do an initial dose and then weekly maintenance doses thereafter? I'd like to get more data on this PolyQuat use (and Borates as well as this has also helped some, but not all, pool owners against yellow/mustard algae).

Richard