Fuge is handling Nitrates... but not Phosphates

[Salt1972]

My daughter and I started a refugium on our 125g mixed reef tank in December hoping it would serve as our primary means of nutrient export (in addition to bi-monthly 30g water changes).

It took a while to get flow (Jebao DCS2000) and lighting (Kessil H80 22 hours / day) right.

1. We tried chaeto at first, but didn't see any growth. No recession, but no growth and no real impact on lowering or maintaining NO3/PO4.

2. We added razor caleurpa and got some growth and nutrient export, but not what others were reporting about harvesting and removing.

3. We dosed 2mL of Iron (Randy's Fergon dissolved in RO/DI) twice per week for 2 weeks and the growth took off... but Cyano set in and the LPS and SPS got pretty unhappy about that. So, we stopped dosing Iron.

At this point, our nitrates are stable at 3ppm, but our phosphates remain at .1 - .12. Should we wait a bit longer to see if the caleurpa / chaeto begin to impact the PO4? I'd rather NOT get into GFO, but that does seem a common / popular method.

What say you?

Thanks in advance.

M

 

[Randy Holmes-Farley Verified Community Expert]

Residual phosphate is a common result, probably due to denitrification taking out some fraction of the N.

That is why many people who use refugia (including me) also use binders like GFO.

 

[Salt1972]

Residual phosphate is a common result, probably due to denitrification taking out some fraction of the N.

That is why many people who use refugia (including me) also use binders like GFO.

Thanks Randy. We HAD a triple chamber reactor running a Purigen type media for Nitrates and PhosGuard for PO4 and it wasn't keeping up with export needs. That's when we switched to the refugium instead.

Would a mesh bag of GFO or PhosGuard or ??? in the refugium be sufficient or would you recommend plumbing the reactor in line with the refugium? FWIW- this circuit is separate from the drip trays, mech filters, and return pumps.

 

[Randy Holmes-Farley Verified Community Expert]

The phosphate might not "need" to be lowered, but a media bag of GFO or phosguard (well rinsed) might do it. A rector with GFO will certainly work, but might be overkill and too low of phosphate may be worse than too much.

Purigen isn't really going to do much for nitrate. It is an organic binding material, like GAC.

 

[rockskimmerflow]

I've always found that refugiums require additional nitrate supplementation to allow them to consume the excess phosphate if the hope is to have a total nutrient control system as the final result. If only normal fish foods are added I would never expect a refugium to keep up with the residual phosphate in relationship to it's nitrate consumption. The preference for so many organisms to sequester or convert nitrogen makes it a much harder compound to keep at the proper level than phosphate.

 

[Salt1972]

The phosphate might not "need" to be lowered, but a media bag of GFO or phosguard (well rinsed) might do it. A rector with GFO will certainly work, but might be overkill and too low of phosphate may be worse than too much.

Purigen isn't really going to do much for nitrate. It is an organic binding material, like GAC.

Makes sense.

1. Am I chasing numbers too much trying to lower PO4 from .12 to .03?

2. Is there any truth / caution that the iron dosing (Fergon tablet dissolved in 30mL RO/DI) 2mL 2x per week might trigger a cyano outbreak?

Thank you so much for your help. We've learned A LOT from you and your articles over the last year.

 

[Salt1972]

I've always found that refugiums require additional nitrate supplementation to allow them to consume the excess phosphate if the hope is to have a total nutrient control system as the final result. If only normal fish foods are added I would never expect a refugium to keep up with the residual phosphate in relationship to it's nitrate consumption. The preference for so many organisms to sequester or convert nitrogen makes it a much harder compound to keep at the proper level than phosphate.

OK-- being the noobs that we are, does this mean that if we dosed NO3 (stump remover), our macro algae would accelerate growth and remove the additional NO3 and, as a result, the PO4? Or, are you suggesting that the GFO route is easier and necessary because, under normal circumstances, a refugium / macro will always consume more No3 than phosphates?

 

[rockskimmerflow]

OK-- being the noobs that we are, does this mean that if we dosed NO3 (stump remover), our macro algae would accelerate growth and remove the additional NO3 and, as a result, the PO4? Or, are you suggesting that the GFO route is easier and necessary because, under normal circumstances, a refugium / macro will always consume more No3 than phosphates?

Both work in similar terms to improve your phosphate level from that which is left in residual by an unsupplemented refugium as the primary nutrient export mechanism. Easier depends on your tank and husbandry situation. Some people prefer one over the other, but both methods can be applied with success IME.

 

[Randy Holmes-Farley Verified Community Expert]

IF nitrate is so low that it limits the algae growth, then the algae will not be able to take up any remaining phosphate, regardless of the level. In that case, adding more nitrate can allow more phosphate export.

But I wouldn't have expected that 3 ppm nitrate is low enough for that to happen.

 

[Salt1972]

What brand / method of phosphate binder do you recommend? Phosguard, Rowaphos, BRS GFO, BRS Hi Cap GFO...

 

[Dennis Cartier]

I think you have probably already hit upon your limiting nutrient (and it is not nitrate).

3. We dosed 2mL of Iron (Randy's Fergon dissolved in RO/DI) twice per week for 2 weeks and the growth took off... but Cyano set in and the LPS and SPS got pretty unhappy about that. So, we stopped dosing Iron.

If 2 ml / week is causing cyano, I would try dosing a smaller amount, say 0.5 ml / day to try to spread it out so there is less of a burst. Also dosing it when the fuge is lit, and the tank is not, will give your macro a chance to utilize it before the main lights are on and cyano is active. If you have a dosing pump, I would try to use that, to basically drip the dose in for each fuge cycle.

Dennis

 

[Randy Holmes-Farley Verified Community Expert]

What brand / method of phosphate binder do you recommend? Phosguard, Rowaphos, BRS GFO, BRS Hi Cap GFO...

Any of those are likely fine. I chose to use BRS GFO (tried several of their types) in my system as I did not want added aluminum (any white binders, such as Phosguard).

 

[Salt1972]

I think you have probably already hit upon your limiting nutrient (and it is not nitrate).



If 2 ml / week is causing cyano, I would try dosing a smaller amount, say 0.5 ml / day to try to spread it out so there is less of a burst. Also dosing it when the fuge is lit, and the tank is not, will give your macro a chance to utilize it before the main lights are on and cyano is active. If you have a dosing pump, I would try to use that, to basically drip the dose in for each fuge cycle.

Dennis

Our tank has taken 10-14 days or so to settle back from the last (assumed bacterial bloom). I'm a bit hesitant to resume dosing iron at all... I think we'll try to GFO. Watch... it'll kill our macro algae and spike nitrates. This is like trying to stand on a basketball.

Thanks for the advice.

 

[Bow69]

Residual phosphate is a common result, probably due to denitrification taking out some fraction of the N.

That is why many people who use refugia (including me) also use binders like GFO.

I’m sure you have answered this a million times, but how do you incorporate your GFO in your system?

 

[Randy Holmes-Farley Verified Community Expert]

I’m sure you have answered this a million times, but how do you incorporate your GFO in your system?

I used a BRS reactor.

Before I got that, I mixed GAC and GFO into a cannister filter.