I never used aquaponics but it takes a lot of fish to keep simple plants like basils or parsley. So according to me you could run into a nutrient deficiency issue. I also think that you will not abble to know which nutrients are bring by the fish : you will know the nutrient level but not the nuts composition so maybe you'll have not enough Pk for flowering for exemple. Last thing to me is that you can experiment ph fluctuation due to the plants and the fish needs but it's nothing hard to manage for someone who have fish tanks since a while