Another Phosphate Question

[crabgrass]

I feed heavy (3x auto dry, 2x manual frozen), and run a skimmer, fuge etc + WC weekly.

I see my nitrate creep from 10 - 20 throughout the week until a WC.

Phos stays steady at .20.

If I add a conservative amount of GFO, I can get Phos down to 0.09 after a few days. With it removed, there is no creep, it just bounces right back to 0.2.

This is a newer tank, and I am not super concerned about the numbers (I’d be perfectly fine if the nitrate stayed at 10-20).

I am more curious about the mechanics of the phosphates - is it just leaching / creating an equilibrium with the dry rocks I have in the tank?

 

[Lavey29]

I feed heavy (3x auto dry, 2x manual frozen), and run a skimmer, fuge etc + WC weekly.

I see my nitrate creep from 10 - 20 throughout the week until a WC.

Phos stays steady at .20.

If I add a conservative amount of GFO, I can get Phos down to 0.09 after a few days. With it removed, there is no creep, it just bounces right back to 0.2.

This is a newer tank, and I am not super concerned about the numbers (I’d be perfectly fine if the nitrate stayed at 10-20).

I am more curious about the mechanics of the phosphates - is it just leaching / creating an equilibrium with the dry rocks I have in the tank?

Dry food and coral supplements raise phosphate. Your number is fine if your tank appears good. You can naturally lower the number by moderating the 2 areas I mentioned. My phosphate routinely sits .2 to .4 now with everything in the tank thriving.

 

[crabgrass]

Dry food and coral supplements raise phosphate. Your number is fine if your tank appears good. You can naturally lower the number by moderating the 2 areas I mentioned. My phosphate routinely sits .2 to .4 now with everything in the tank thriving.

Thanks - I was more curious on the phosphate bounce more than anything. Less concerned on control than just understanding the mechanics.

 

[jda]

Aragonite binds po4. It can also unbind. As the water level po4 lowers, the aragonite unbinds. As the water level rises, the aragonite binds more. This is a bind/unbind type of deal and not a absorb/leach - there are rules mostly around the level of po4 in the water column, but also salinity and temperature matter a bit too.

At low water levels, the aragonite acts as a buffer that never really lets you get to true zero (you have to REALLY be aggressive with media or chemicals). At higher water levels of po4, the aragonite is a large reservoir that is hard to remove.

You just have to keep removing the po4 from the water column and the aragonite will release and the levels will come down eventually, but it is slow. ...like if you do this a few more times, you might notice that you settle back at 0.19 or 0.18 when it settles back.

 

[crabgrass]

Aragonite binds po4. It can also unbind. As the water level po4 lowers, the aragonite unbinds. As the water level rises, the aragonite binds more. This is a bind/unbind type of deal and not a absorb/leach - there are rules mostly around the level of po4 in the water column, but also salinity and temperature matter a bit too.

At low water levels, the aragonite acts as a buffer that never really lets you get to true zero (you have to REALLY be aggressive with media or chemicals). At higher water levels of po4, the aragonite is a large reservoir that is hard to remove.

You just have to keep removing the po4 from the water column and the aragonite will release and the levels will come down eventually, but it is slow. ...like if you do this a few more times, you might notice that you settle back at 0.19 or 0.18 when it settles back.

This is super helpful and I think answered my question. So basically, IF I chose to remove it via GFO, it’s probably going to be a long process to tick down to get to baseline levels. As to @Lavey29 point, there are also other variables I am adding (dry food, occasional coral foods, etc.), that would obviously influence it as well.

 

[jda]

Sure. You are always adding more po4, but not likely at the rate that you can remove it with media.

The po4 binding to aragonite is exponential. The more po4 that you have, the more binds to the rocks and sand. At fairly high po4 levels in the water, you can have a massive amount in the rock and sand. I did an experiment with some CaRx media in a reactor in a 10g tank and over 50ppm of po4 got down to like 0.16 in the water column. Crazy right? This is why I am SOOOOO amazed that people wand to add po4 to their tanks when they have some already - most of them don't know they are just storing it in their rocks to deal with later.

GFO has the same kind of exponential binding characterists with the water column. If you lower the water column po4 level with a water change, then po4 will unbind from GFO and even Aluminum Oxide.

 

[Randy Holmes-Farley Verified Community Expert]

I am more curious about the mechanics of the phosphates - is it just leaching / creating an equilibrium with the dry rocks I have in the tank?

Most likely, yes.

 

[crabgrass]

Sure. You are always adding more po4, but not likely at the rate that you can remove it with media.

The po4 binding to aragonite is exponential. The more po4 that you have, the more binds to the rocks and sand. At fairly high po4 levels in the water, you can have a massive amount in the rock and sand. I did an experiment with some CaRx media in a reactor in a 10g tank and over 50ppm of po4 got down to like 0.16 in the water column. Crazy right? This is why I am SOOOOO amazed that people wand to add po4 to their tanks when they have some already - most of them don't know they are just storing it in their rocks to deal with later.

GFO has the same kind of exponential binding characterists with the water column. If you lower the water column po4 level with a water change, then po4 will unbind from GFO and even Aluminum Oxide.

Makes sense. And yea, every time I “bottomed out” or significantly lowered P with GFO, it feels likes an elastic band and rebounds to original number within a day of GFO removal. I sort of thought it was testing errors, but the pattern is so consistent now I don’t feel like it’s a user issue as much as equilibrium in the tank. If it was foods, etc, I would have expected a slow creep like I see with my Nitrate levels

Again, I am not overly concerned with my numbers (corals are happy and growing new heads), was just curious if I thought was observing had some science behind it.

Thanks!