it looks to me like you're using a super phosphate (something with a ...- (40-60) -......
these ferts are NO GOOD for pot, they're made for fruiting plants and roses. using a super p regularly will cause a p overload, which will alter ph and end up locking p and k out. (ask how i know...) leaves end up crispy and dead, though the plants are still growing.
i could be wrong, but if i'm not, keep flushing, and use light regular nutes with a level npk.