Reaching a concentration of PO4 above 2.4 ppm with Seachem's flourish is a PIMA. I would like to add more, better phosphate - stop GSA outbreaks. Maybe 2.4 ppm is Ok; I don't know. Would a PO4 concentration of 10 ppm be a problem?
10 ppm of PO4 probably won't harm the tank occupants, but it is way more than the plants need. Increased PO4 dosage to try to head off GSA isn't a bad idea, in my opinion, but it doesn't take that much PO4 to be effective.