Don't forget the other side of the equation. I could well be a bumper crop of FA due to conditions and the tilapia ate a bunch but simply could not keep up.
Another great point, that also reminds me of grass carp issues we have. Sometimes the grass carp will find a rooted vegetation they like, and ignore the FA.
I'd be interested to know if the pond in question had some additional rains earlier in the year which may have brought in some additional nutrients. There's also a chance that the pond is simply aging, with increased nutrient loading.
