[Randy Holmes-Farley]

Sand beds do when you throw them off that far.

I don't know what that sentence means, but you apparently ignored the fact that the macroalgae may be able to take up some slack of excess phosphate.

Nevertheless, I quite agree and have said for years that the fact of reducing nitrate and not phosphate does negatively impact the ability to reduce phosphate in biological ways, such as macroalgae.

Luckily, my macroalgae is far more efficient at removing both N and P than is the sand bed under them in my refugium, so that seems to not be an issue, at least in my aquarium.