Based on your question, it doesn't seem as though you're understanding the relationship between CYA and FC thoroughly, which is probably the most important tenet of TFPC. Please read or re-read the "pool school" e-book. Click on this link;
Pool School - Trouble Free Pool ; scroll to the bottom of the page; download the free e-book on a popular app like Google or Amazon; and read or re read the short e-book to get a full understanding of this all-important relationship.
If you've read through the pool school e-book and understand CYA's role in preventing algae, you'd know that a CYA level that this group considers too high (that is anything above 90) is such that keeping FC high enough to be effective in preventing algae would be impractical. For instance, if CYA were 200 in a manually-chlorinated pool and one extrapolated the math that is used to create the chlorine/cya chart, then one would need to target and dose FC all the way up to 17-19 ppm daily to ensure that the FC level never dropped below 15. Otherwise, the FC level would be too low to be effective at that CYA level, and if there were some sort of algae outbreak that occurred at this hypothetically-high CYA level for either an SWCG or manually-chlorinated pool, one would have to SLAM maintaining an FC level of 80, which would require massive amounts of liquid chlorine to reach and maintain that level. You won't see those kind of numbers in the TFP charts, because TFP recommends drain/refill above CYA 90, which is way below 200, and this is because anything above CYA 90 is an impractical way to manage a chlorinated pool.
A CYA level that is too low, in a way, is a different sort of problem. The proper CYA level (30-50 for manually-dosed pools and 70-80 for SWCGs) is the optimal ranges to protect accelerated FC loss to UV rays. So the problem with CYA that is "too low" is that any chlorine that you add to bring FC up to an acceptable level for preventing algae, whether it's added manually or via an SWCG, could be quickly lost during daylight hours and your pool could be sitting at or near FC 0 at any given time, and that's a situation you never want even for a second. So even though the required minimum FC level is lower for a pool that has a lower CYA level, you still must never drop below a minimum FC level, and that minimum level is always higher than zero regardless of the CYA level. But like it has already been answered, the CYA level by itself does not cause algae whether its too high or too low. It's has more to do with CYA's effect on how chlorine works or doesn't work in your pool to prevent algae.
