Nutrient Export

SantaMonica · Jul 17, 2025

What do all algae (and cyano too) need to survive? Nutrients. What are nutrients? Ammonia/ammonium, nitrite, nitrate, phosphate and urea are the major ones. Which ones cause most of the algae in your tank? These same ones. Why can't you just remove these nutrients and eliminate all the algae in your tank? Because these nutrients are the result of the animals you keep.

So how do your animals "make" these nutrients? Well a large part the nutrients comes from pee (urea). Pee is very high in urea and ammonia, and these are a favorite food of algae and some bacteria. This is why your glass will always need cleaning; because the pee hits the glass before anything else, and algae on the glass consume the ammonia and urea immediately (using photosynthesis) and grow more. In the ocean and lakes, phytoplankton consume the ammonia and urea in open water, and seaweed consume it in shallow areas, but in a tank you don't have enough space or water volume for this, and, your other filters or animals often remove or kill the phytoplankton or seaweed anyway. So, the nutrients stay in your tank.

Then, the ammonia/ammonium hits your rocks, and the periphyton on the rocks consumes more ammonia and urea. Periphyton is both algae and animals, and is the reason your rocks change color after a few weeks from when they were new. Then the ammonia goes inside the rock, or hits your sand, and bacteria there convert it into nitrite and nitrate. However, the nutrients are still in your tank.

Also let's not forget phosphate, which comes from solid organic food particles. When these particles are eaten by microbes and clean up crews, the organic phosphorus in them is converted into phosphate. However, the nutrients are still in your tank.

So whenever you have algae or cyano "problems", you simply have not exported enough nutrients out of your tank compared to how much you have been feeding (note: live rock can absorb phosphate for up to a year, making it seem like there was never a problem. Then after a year, there is a problem).

So just increase your nutrient exports. You could also reduce feeding, and this has the same effect, but it's certainly not fun when you want to feed your animals :)

Randy Holmes-Farley · Jul 17, 2025

I don’t agree with a number of aspects of this analysis.

Lowering nutrients is not the best way to control algae since it typically risks not having enough nutrients for corals.

Cyano, being a bacteria, can get all the N and P and energy it needs from organics.

Phosphate is excreted by fish and many other organisms. It does not just come from particulates.

Garf · Jul 17, 2025

SantaMonica said:
What do all algae (and cyano too) need to survive? Nutrients. What are nutrients? Ammonia/ammonium, nitrite, nitrate, phosphate and urea are the major ones. Which ones cause most of the algae in your tank? These same ones. Why can't you just remove these nutrients and eliminate all the algae in your tank? Because these nutrients are the result of the animals you keep.

So how do your animals "make" these nutrients? Well a large part the nutrients comes from pee (urea). Pee is very high in urea and ammonia, and these are a favorite food of algae and some bacteria. This is why your glass will always need cleaning; because the pee hits the glass before anything else, and algae on the glass consume the ammonia and urea immediately (using photosynthesis) and grow more. In the ocean and lakes, phytoplankton consume the ammonia and urea in open water, and seaweed consume it in shallow areas, but in a tank you don't have enough space or water volume for this, and, your other filters or animals often remove or kill the phytoplankton or seaweed anyway. So, the nutrients stay in your tank.

Then, the ammonia/ammonium hits your rocks, and the periphyton on the rocks consumes more ammonia and urea. Periphyton is both algae and animals, and is the reason your rocks change color after a few weeks from when they were new. Then the ammonia goes inside the rock, or hits your sand, and bacteria there convert it into nitrite and nitrate. However, the nutrients are still in your tank.

Also let's not forget phosphate, which comes from solid organic food particles. When these particles are eaten by microbes and clean up crews, the organic phosphorus in them is converted into phosphate. However, the nutrients are still in your tank.

So whenever you have algae or cyano "problems", you simply have not exported enough nutrients out of your tank compared to how much you have been feeding (note: live rock can absorb phosphate for up to a year, making it seem like there was never a problem. Then after a year, there is a problem).

So just increase your nutrient exports. You could also reduce feeding, and this has the same effect, but it's certainly not fun when you want to feed your animals :)

Algae grows just fine in the ocean with phos and nitrate at barely or non detectable levels with hobby test kits. Have you heard of "Grazing Halos"?

Halo Patterns Around Coral Reefs May Signal Resilience | Dartmouth

home.dartmouth.edu

Randy Holmes-Farley · Jul 17, 2025

Garf said:
Algae grows just fine in the ocean with phos and nitrate at barely or non detectable levels with hobby test kits. Have you heard of "Grazing Halos"?

Halo Patterns Around Coral Reefs May Signal Resilience | Dartmouth

home.dartmouth.edu

Yes, that’s my point. One needs to reduce nutrients too low to make that a good plan to control algae. :)

Herbivores are a far better way to control algae, as they do in the ocean.

CHSUB · Jul 17, 2025

Controlling algae is not a single edge knife…it’s a multiple edge knife. Low nutrients (for a number of reasons, including coral health), consumers, flow, space, and manual removal. Corals do best with ocean level nutrients and combining that with other listed controls, I can guarantee you will not worry about nuisance algae….

This coral has grown well in 6 months and doesn’t rely on algae for food, Ime, there can be enough food in a glass box where inorganic nutrients are not relied on….