Phosphates, the Phantom Menace

[charterreefer]

I have phosphates in my tank. I can't measure them but I know they are there. It is appearing as red slimy patches in my refugium. I have looked out in google land but can't find any info for how to treat with GFO - when you can't measure anything! How much and most importantly how often must it be changed?? ( I have 300 total gals of water and started with 1 1/2 cups GFO as to not shock my system).
All the articles say - if you measure a rise in PO4 your GFO is exhausted and won't work anymore. That's fine if you can measure PO4 levels but I guess I will use the "force" and just feel it's presence. Or better yet, if I can see it (the red stuff) I can kill it.
From starting to use GFO a few weeks ago I noticed that the water looks "clearer" ( it has that polished look you get when using the GFO) but the red stuff is still there. For now I am going to change it every week until I have the cyano on the run. It's an all SPS tank. I'm closely monitoring them for any signs of stress. So far so good.

I always did 10% weekly water changes but never used GFO. My fish load is small and I only feed once or twice a day. I keep NO3 at ~ 1ppm in an attempt to keep the Redfield ratio in check.
Apparently, it was a good experiment that determined water changes alone do not address the continual buildup of PO4.

Is the PO4 level always undetectable once cyano is growing in a system?

I have a funny feeling this is going to take a long time to undo. As I remove the PO4 from the system it's apparently leaching back into the water column from the rocks.

Any thoughts? Does this sound like I am treating this correctly?

 

[horseplay]

If you're trying to strip your water of PO4 thus stopping the growth of cyano, your corals will suffer first. So it's not a good strategy.

A proven strategy is to keep the nutrient levels, NO3 and PO4 at around the redfield ratio, about 1ppm and 0.03ppm.

As for your cyano outbreak, use chemi clean it will be gone in 2 days.

 

[redfishbluefish]

The other consideration is that our test kits only measure inorganic phosphate (phosphorus, orthophosphate). They do not measure organic phosphate compounds, which there are many. So you simply might not be "seeing" that phosphate in your tank......but the algae sure does!

Are you running a skimmer? Because here's the kicker.....a skimmer will remove organic phosphates, but not inorganic. So if you're running a skimmer, the phosphates we don't know are there are being removed.

 

[charterreefer]

Yes, I am running a large reef octopus elite in the system, it's a beast, slightly oversized. Been there since the beginning. I feel running 1 1/2 cups of normal strength brs type gfo should be a safe level and that changing it every week should ensure that it's not just sitting there saturated, doing nothing. I was thinking of going up to 1 1/2 cups of the Stronger brs gfo in 3 more weeks, after the corals have gotten used to the lower Po4 levels. Then changing every 4 weeks or so (while watching for signs of algae)