Stubborn .16 Phosphate

[James MacFarlane]

Hi all!

I think I may have a redfield ratio issue. Randy, I've read everything you've ever written, thank you for your contribution to this hobby.

I have phosphate that I cannot get below .16. I use RO/DI, and have tested it out of the unit at 0.

I run a skimmer (wet), 12"x 12" scrubber, feed 3 times a week. I also keep chaeto in my sump. I have no algae at all, in fact, I cleaned the scrubber screen 72 hours ago, and have no algae growth. I also have very little skimmate. Slow but steady coraline growth.

Tank is a standard 65g.

My parameters are as follows (all per RedSea Pro kits) -
Ammonia - 0
Nitrite - 0
Nitrate - 0
Phosphate - .16
Ca - 520
Kh - 10
Magnesium - 1360

Thanks to anyone who offers an opinion!

 

[120reefkeeper]

Faulty phosphate test??

 

[Downbeach]

I would get a second opinion on the PO4 kit, hopefully with a Hanna checker.

 

[James MacFarlane]

Thanks all, I may have to take a look at the Hanna. I also have a Seachem Phosphate test, but it's horrible.

 

[Randy Holmes-Farley]

It is certainly possible that the ATS is nitrogen limited, and if so, dosing some nitrate may help.

 

[Kungpaoshizi]

Redfield ratio isn't about the carbon-bacteria tangents, but it's close enough to compare. But if you're not carbon dosing, it doesn't matter.
One thing that works quite well ime is the nopox+reef energy combo. Carbon dosing and feeding a lot of nitrates(that's also food as compared to ONLY adding nitrate) works quite well to keep phosphate down.

Have you always dealt with this or perhaps it's a new group of rocks that's leaching? Do you switch up foods to prevent the same elements being introduced?

 

[dbrewsky]

According to the ratio, phosphate is the least utilized element, meaning for every 16 parts of nitrogen only 1 part phosphorus will be utilized. Their is quite possibly a nitrogen limitation, however, you would have to continue to add large amounts of nitrate over time to utilize this ratio to reduce your phosphate using this theory. I would ask yourself these questions:

1 Is my phosphate test reading accurate? Can i cross reference with at least one other test to confirm ballpark readings?

2 Am I seeing a actual issue directly related to phosphate? Do I need to chase a number if the tank is healthy and corals happy?

3 What are my best methods to drop this number based on question #2? Is it best to add a nutrient do drop another? Is there another method to remove the phosphate in this situation rather than relying on Redfield ratio utilization?

If it were me and my tank seemed healthy, I would verify I am getting phosphate readings in the same ballpark on a new test kit or batch of reagents. If those results coincide and corals are showing good color and growth, I would not concern myself and just monitor over time and make slow adjustments if necessary.

If there was a issue with the health of my corals, I would not rely on adding extra nitrate as a method to remove the phosphorous source as it would take a large amount relatively to reduce the phosphate levels following this rule. I would look into larger, frequent water changes to bring these levels down safely before considering other phosphate binding medias/chemicals. Your system is out of balance and until you bring it back you will continue to have issues and phosphate will continue to build up. The best way to reset a system is physically removing the imbalance and restoring your desired parameters.

This was a concept that I did not fully understand until I started keeping high-tech freshwater planted tanks which relies heavily on these principles. Its amazing how an aquarium properly balanced according to the Redfield ratio will not grow any algae even though nitrogen and phosphorus are through the roof. As soon an imbalance occurs, algae takes of like wildfire and the actual limiting element can often be easily diagnosed by the type of algae present.

 

[Randy Holmes-Farley]

According to the ratio, phosphate is the least utilized element, meaning for every 16 parts of nitrogen only 1 part phosphorus will be utilized. Their is quite possibly a nitrogen limitation, however, you would have to continue to add large amounts of nitrate over time to utilize this ratio to reduce your phosphate using this theory. I would ask yourself these questions:

1 Is my phosphate test reading accurate? Can i cross reference with at least one other test to confirm ballpark readings?

2 Am I seeing a actual issue directly related to phosphate? Do I need to chase a number if the tank is healthy and corals happy?

3 What are my best methods to drop this number based on question #2? Is it best to add a nutrient do drop another? Is there another method to remove the phosphate in this situation rather than relying on Redfield ratio utilization?

If it were me and my tank seemed healthy, I would verify I am getting phosphate readings in the same ballpark on a new test kit or batch of reagents. If those results coincide and corals are showing good color and growth, I would not concern myself and just monitor over time and make slow adjustments if necessary.

If there was a issue with the health of my corals, I would not rely on adding extra nitrate as a method to remove the phosphorous source as it would take a large amount relatively to reduce the phosphate levels following this rule. I would look into larger, frequent water changes to bring these levels down safely before considering other phosphate binding medias/chemicals. Your system is out of balance and until you bring it back you will continue to have issues and phosphate will continue to build up. The best way to reset a system is physically removing the imbalance and restoring your desired parameters.

This was a concept that I did not fully understand until I started keeping high-tech freshwater planted tanks which relies heavily on these principles. Its amazing how an aquarium properly balanced according to the Redfield ratio will not grow any algae even though nitrogen and phosphorus are through the roof. As soon an imbalance occurs, algae takes of like wildfire and the actual limiting element can often be easily diagnosed by the type of algae present.

I would just caution that algae in seawater is often very different and extrapolating from fresh water can be misleading. CO2 is often the limiting nutrient in fresh water, but often not in seawater because many algae (and corals, etc) get CO2 from bicarbonate, which is fairly plentiful in seawater.

Consequently, N and P are often limiting in the ocean and in reef tanks. Sometimes iron can be limiting. But it is not generally the case that having elevated N and P in seawater can preclude an algae problem just by having them at a specific ratio. For example, once nitrate or phosphate rise in seawater, they no longer limit algae growth, and so it doesn't matter so much what the value if there is already "enough".

 

[rock_lobster]

Could be leaching from your rocks or sand.

 

[toothybugs]

I will second and stand behind randy's suggestion - I would snag a little KNO3 off Amazon (Spectracide) and look to bump your NO3 values to 2-3ppm. It won't hurt anything, will be readily consumed, and if it helps your Redfield you will see a drop in PO4 with only a modest presence of NO3.

Edit: You can use PhosGard or GFO or the like, but KNO3 is cheap by comparison. You don't need a reactor, for one, and two, it's generally nicer to go 'natural' vs more stuff you don't necessarily need to buy.

 

[James MacFarlane]

Wow, thank you all for your thoughtful responses. I've been doing 5 gallon changes each week, and may try to bump that up.

Everything looks great for now, so I have the luxury of approaching this with purpose and planning. If the larger changes don't get me below .04, then I will add more food ect, and greater variety as suggested.

Rock is all less than a year old, so that may be a factor?

I also have a reactor Im not using. Worth trying GFO? Is there a preferred type/brand?

Thanks again everyone!

 

[Kungpaoshizi]

Apologies btw, I forgot to add the link..

Redfield ratio or Redfield stoichiometry is the atomic ratio of carbon, nitrogen and phosphorus found in phytoplankton and throughout the deep oceans.
https://en.wikipedia.org/wiki/Redfield_ratio