Phosphate in dry rock

[CatsandClowns]

Heyo! Ive been using GFO for a while and have made good progress over the past month. After my most recent water change, I noticed 48 hours later that PO4 was just about the same as it had been before the WC. This is a bit different then recorded from previous water changes, PO4 would rebound by at least 0.05-0.1ppm 48 hours after. Is this a sign that the dry rock I started off with is depleting its stored phosphate? Using Rowaphos, how slowly should I expect it to decrease from here on, and without the use of a reactor, how frequently should I change it, compared to previously every 3 days at a higher concentration?

 

[Mr. Mojo Rising]

It does sound like its coming from the rocks. It took me well over a year of heavy gfo use to finally get it down. Its unknown how much phosphate is stored in the rocks, it could take weeks or months to absorb it out.

 

[Randy Holmes-Farley Verified Community Expert]

Yes. The phosphate is bound to the rock surface, and every time you remove some, the new equilibrium concentration with the water will be lower.

Is the rock in a reef tank, or some sort of holding bin? If the latter, I’d strip it out fast with lanthanum.

 

[KrisReef]

Your description of a zero or soft rebound does suggest that you have removed much of the phosphate that was bound to the dry rock.

How fast should you adjust your gfo or Rowaphos use only the Lord knows, but keep close watch with your testing because it can quickly go to zero once the surplus has been sequestered. It seems you are there. GL.

 

[Arkayology]

If you drop the rock in my tank the phos will be gone in 24 hours lol. My tank cannot get enough. I think it might be the dry rock I used, but I am not 100%.

 

[dvgyfresh]

If you drop the rock in my tank the phos will be gone in 24 hours lol. My tank cannot get enough. I think it might be the dry rock I used, but I am not 100%.

it’s soaking it up to give you the problem down the road , aren’t rocks nice

 

[Randy Holmes-Farley Verified Community Expert]

Rocks can come with zero, some, or a lot of phosphate. After they soak in a fixed concentration of phosphate, they will come to the same equilibrium before long. :)

 

[Arkayology]

it’s soaking it up to give you the problem down the road , aren’t rocks nice

Yup. It will happen sooner or later!