Hi. If I'm reading you correctly, you're saying that your phosphate is up to 2.5 ppm. That's very high for sure. What is your nitrate? If it is also very elevated, you want to use a technique that will decrease them both, like a bigger algae scrubber, carbon dosing and/or water changes. If it's just the phosphate that's really high and your nitrate is ok, granular ferric oxide (GFO) in a fine mesh bag in a reactor would help bring phosphate down.