Where have all the phosphates gone

[watchguy123]

My understanding is that too reduce or control phosphates, you must either manage it 1) chemically eg GFO 2) biologically eg. Chaeto or bacteria carbon dosing 3) physically eg skimmer or water changes which is very inefficient

There are also new approaches like siporax which allows for bacterial colonization on its surface like rock except much more porous and therefore more colonizable surface area.

The issue I have is that I recognize how nitrate is both reduced and controlled by these various methods but I'm not clear about phosphates. I appreciate the redfield ratio or at least that nitrates get consumed at a much larger ratio than phosphates. And I appreciate those that carbon dose can drive nitrates to zero or near zero and that nitrate dosing with carbon dosing can drive phosphates down also. I also understand that there may be potential reservoirs for phosphates eg. Rock and sand bed.



In my experience chaeto, water changes, skimming can keep nitrates below 10ppm fairly predictably. Adding siporax seems to drive the nitrates less than 2 ppm. But my phosphates may range from .07 to .15 ppm (Hanna ulra low phosphorus) unless I add GFO. I follow so many threads on r2r where reefers manage low phosphates without carbon dosing and often without GFO.

What I do not understand are those that don't carbon dose, how do they manage low phosphate levels?

 

[LBehr]

The guys who I've seen do it don't have fish or only have one or two and feed very little and have very powerful skimmers.

 

[Randy Holmes-Farley Verified Community Expert]

Denitrification media in general are not very effective at phosphate control. The only export of phosphate is when bacteria take it up and then are either skimmed out, are eaten by something, or remain alive in the water. The same holds true for organic carbon dosing, but it does somewhat better because aerobic bacteria use more P relative to N than do low O2 bacteria.

Other ways to control phosphate include just making sure your tank organisms are taking in all the N and P that you add in foods. So tha tmeans a high load of photosynthetic organisms relative to those you have to feed.

 

[Oceansize]

My impression has always been that those who keep phosphates at or below 0.03 WITHOUT using GFO or a well-disciplined water change regimen must be employing well-tuned refugiums/macro algae. But you are using chaeto and doing water changes and still not getting phosphates below 0.07, which would indicate that GFO really is the best remaining option to reduce phosphates to 0.03.

I don't have space for a refugium so they are out of the question for me, and I don't like the look of macro in my DT. I do not carbon dose for nitrate export because I feel the sulphur denitrator is a far superior solution. Therefore I feel like GFO is my only option for effective phosphate reduction, assuming that 0.03 is the goal.