I don't have a PO4 test kit, so I have no idea what's going on in our 120g. However, there are various macroalgae growing well in the tank, which, combined with loads of light, I am assuming is consuming lots of PO4 and nitrate.

I also do 15% water changes, BB siphoning, and mechanical fitration cleaning weekly. But I doubt that changing such a small amount of water does much to reduce any nutrient could be in my tank. Say, for instance, I had 10 ppm nitrate in there. A 15% water change will only reduce the nitrate to 8.5 ppm. And by the next week, more nitrate will have been added to the water, so I'd probably still have 10 ppm.

All I've got to say is using non-invasive macroalgae to soak up nutirents is the most natural and cheapest way to go.

Am using RO/DI water, btw.

That would be true to an extent. Halimeida does use phosphates in growth, it simply builds more of its structure from calcium than some other algaes.

Edit:

I guess I should answer the thread's question... haha!

I cant select any of those options above. I have tested the phosphates and got a 0 on the kit.. but ofcourse most kits arent the best. My only method of phosphate reduction right now, if there is any, is use of a refugium. I am considering using a VERY small amount of phosban on the next system, but just for the heck of it, the fuge will be huge anyways, and with a low fishload, high floow, good skimming, I dont see it being an issue.

Woops... *Haliemeda does use Phosphorous(not phosphates, but the use of phosphorous would break down the phosphates into oxygen and phosphorous).*

Aha... correction again, I believe they simply directly take in phosphate rather than phosphorous. ATP(Adenosine Triphosphate) is the molecule used to store energy. I cannot quite remember whether plants absorb phosphorous or phosphate when producing PGAL.

This is what I was led to believe, and after I started using the phosfate reactor it was drastically reduced from a thriving jungle to where I have to really look to find some in my tank.