Phosphate reduction filling. This product takes your phosphate down to around 20% of its current level. So, if you have a 1ppm fresh from the tap it will drop it around to 0.2ppm. If this is on a top up this will help stop major blooms of blanket weed in the pond.
Plants in the pond will also use phosphate for food. In a large pond where Acute as already dropped the level, 0.2ppm topping up won’t be able to raise the overall ppm in the pond before plants use it for food.