How fast does macro-algae lower phosphates?

[Zaxh]

Does anyone have any type of idea of how fast macro algae lowers phosphates? Just a ball park range. Let’s say 10 gallon tank with 1.0 phosphates and using dragon breath macro (not my actual test lol) to .05.

Would it be a course of a few weeks, months? Quarters?

Currently my tank has .17 phos and 24 ppm nitrate. Anyone have any experience ?

 

[fish farmer]

Does anyone have any type of idea of how fast macro algae lowers phosphates? Just a ball park range. Let’s say 10 gallon tank with 1.0 phosphates and using dragon breath macro (not my actual test lol) to .05.

Would it be a course of a few weeks, months? Quarters?

Currently my tank has .17 phos and 24 ppm nitrate. Anyone have any experience ?

Several months, but I saw significant growth in a couple months. I have a sumped 29 gallon with 20 year old live rock. I was also siphoning out algae with routine WCs, skimmer and brief GFO use.

I started with 40ppm N and 2ppm P, September 2018. I was getting reduction and double chaeto growth into December, readings were 15ppm N and 0.5ppm P.

Into 2019, Nitrates started to stabilize around 5ppm, phosphates were 0.3 to 0.7 ppm.

It wasn't until 2020 that I noticed very low nitrate and phosphates, chaeto was slowing down growth as well.

 

[danimal1211]

Several factors to consider that will determine results: how much algae you have, how intense is it’s lighting, how much flow is it getting. If you have a small bit in display, you may never see a noticeable reduction, however, if you have a well sized refugium, it can manage nutrient export quite well.
You can go too far with it as well, I attempted a chaeto reactor on my 10 gallon and it stripped the nutrients to undetectable levels in less than 48 hours. It was way too much.

 

[ninjamyst]

.17 phosphate is fine. Don't go chasing numbers.

 

[Randy Holmes-Farley]

Does anyone have any type of idea of how fast macro algae lowers phosphates? Just a ball park range. Let’s say 10 gallon tank with 1.0 phosphates and using dragon breath macro (not my actual test lol) to .05.

Would it be a course of a few weeks, months? Quarters?

Currently my tank has .17 phos and 24 ppm nitrate. Anyone have any experience ?

It's an extraordinarily difficult thing to say based on time since you likely do not know how much phosphate you are adding each day, and how much is presently bound to rock and sand that you'd have to strip as you lower phosphate (which may be far more than is actually in the water at one time).

But it is relatively easy to know how much N and P is taken up by a fixed amount of growth of macroalgae:

Phosphate in the Reef Aquarium

The phosphorus atom is one of living matter's basic building blocks. It is present in every living creature and in every reef aquarium's water. Unfortunately, it is often present in excess in reef aquaria, and that excess has the potential to cause at least two substantial problems for...

www.reefedition.com

Phosphate Export by Organisms: Macroalgae

As mentioned above, growing and harvesting macroalgae can be a very effective way to reduce phosphate levels (along with other nutrients) in reef aquaria. In my reef system, where I have large, lit refugia to grow the macroalgae Caulerpa racemosa and Chaetomorpha sp., these algae are clearly a significant phosphate export mechanism. Aquaria with large amounts of thriving macroalgae can avoid microalgae problems or excessive phosphate levels that might inhibit coral calcification. Whether the reduction in phosphate is the cause of the microalgae reduction is not always obvious; other nutrients can also become limiting. But to reef aquarists with a severe microalgae problem, the exact mechanism may make no difference. If rapidly growing macroalgae absorb enough phosphorus to keep the orthophosphate concentrations in the water column acceptably low, and at the same time keep microalgae under control, most reefkeepers will be satisfied.

For those interested in knowing how much phosphorus is being exported by macroalgae, this free PDF article in the journal Marine Biology has some important information. It gives the phosphorus and nitrogen content for nine different species of macroalgae, including many that reefkeepers typically maintain. For example, Caulerpa racemosa collected off Hawaii contains about 0.08% phosphorus by dry weight and 5.6% nitrogen. Harvesting 10 grams (dry weight) of this macroalgae from an aquarium would be the equivalent of removing 24 mg of phosphate from the water column. That amount is the equivalent of reducing the phosphate concentration from 0.2 ppm to 0.1 ppm in a 67-gal. aquarium. All of the other species tested gave similar results (plus or minus a factor of two). Interestingly, using the same paper’s nitrogen data, this would also be equivalent to reducing the nitrate content by 2.5 grams, or 10 ppm in that same 67-gal. aquarium.

 

[Zaxh]

It's an extraordinarily difficult thing to say based on time since you likely do not know how much phosphate you are adding each day, and how much is presently bound to rock and sand that you'd have to strip as you lower phosphate (which may be far more than is actually in the water at one time).

But it is relatively easy to know how much N and P is taken up by a fixed amount of growth of macroalgae:

Phosphate in the Reef Aquarium

The phosphorus atom is one of living matter's basic building blocks. It is present in every living creature and in every reef aquarium's water. Unfortunately, it is often present in excess in reef aquaria, and that excess has the potential to cause at least two substantial problems for...

www.reefedition.com

Phosphate Export by Organisms: Macroalgae

As mentioned above, growing and harvesting macroalgae can be a very effective way to reduce phosphate levels (along with other nutrients) in reef aquaria. In my reef system, where I have large, lit refugia to grow the macroalgae Caulerpa racemosa and Chaetomorpha sp., these algae are clearly a significant phosphate export mechanism. Aquaria with large amounts of thriving macroalgae can avoid microalgae problems or excessive phosphate levels that might inhibit coral calcification. Whether the reduction in phosphate is the cause of the microalgae reduction is not always obvious; other nutrients can also become limiting. But to reef aquarists with a severe microalgae problem, the exact mechanism may make no difference. If rapidly growing macroalgae absorb enough phosphorus to keep the orthophosphate concentrations in the water column acceptably low, and at the same time keep microalgae under control, most reefkeepers will be satisfied.

For those interested in knowing how much phosphorus is being exported by macroalgae, this free PDF article in the journal Marine Biology has some important information. It gives the phosphorus and nitrogen content for nine different species of macroalgae, including many that reefkeepers typically maintain. For example, Caulerpa racemosa collected off Hawaii contains about 0.08% phosphorus by dry weight and 5.6% nitrogen. Harvesting 10 grams (dry weight) of this macroalgae from an aquarium would be the equivalent of removing 24 mg of phosphate from the water column. That amount is the equivalent of reducing the phosphate concentration from 0.2 ppm to 0.1 ppm in a 67-gal. aquarium. All of the other species tested gave similar results (plus or minus a factor of two). Interestingly, using the same paper’s nitrogen data, this would also be equivalent to reducing the nitrate content by 2.5 grams, or 10 ppm in that same 67-gal. aquarium.

Out of curiosity. I am upgrading from an AIO to a tank with a sump. Can I refurbish a Kessil A80 to use as a refugium light? Thoughts?

 

[Randy Holmes-Farley]

Out of curiosity. I am upgrading from an AIO to a tank with a sump. Can I refurbish a Kessil A80 to use as a refugium light? Thoughts?

Sorry, I don't know anything about the intensity of that light, but almost any light is suitable, and the more intense it is (until you get super intense), the faster it may drive photosynthesis.