"Nutrients" Basic Question

CastAway · Jul 22, 2015

When it comes to "nutrients" of nuisance algae in a display, which is more influential, nitrate or phosphate?

For example, if I want to keep my nitrate up a little, for the sake of the zooxanthellae in my SPS, is eliminating PO4 my primary means of eliminating nuisance algae? I'm wondering, and I may be confusing myself here, but where is that threshold between healthy algae I want and healthy algae I don't want?

Randy Holmes-Farley · Jul 22, 2015

CastAway said:
When it comes to "nutrients" of nuisance algae in a display, which is more influential, nitrate or phosphate?

For example, if I want to keep my nitrate up a little, for the sake of the zooxanthellae in my SPS, is eliminating PO4 my primary means of eliminating nuisance algae? I'm wondering, and I may be confusing myself here, but where is that threshold between healthy algae I want and healthy algae I don't want?

Algae (either microalgae or macroalgae) MUST have a suitably high concentration of phosphate, a nitrogen source (such as ammonia or nitrate) and a variety of trace elements such as iron, molybdenum, etc..

If any of those is low enough that the organism cannot get enough, then it will grow slowly or not at all (even die). If any of them are at least at the level where the plant gets enough, then having more doesn't typically make it grow even faster (at least beyond a reasonable point in the transition zone from being a limiting nutrient to not being limiting). The exact threshold depends both on the species and on the levels of the other nutrients.

In the ocean, the limiting nutrient is iron in some locations, and for different algaespecies, can be either N or P limited in the same location.

acbaldwin · Jul 22, 2015

Randy Holmes-Farley said:
Algae (either microalgae or macroalgae) MUST have a suitably high concentration of phosphate, a nitrogen source (such as ammonia or nitrate) and a variety of trace elements such as iron, molybdenum, etc..

If any of those is low enough that the organism cannot get enough, then it will grow slowly or not at all (even die). If any of them are at least at the level where the plant gets enough, then having more doesn't typically make it grow even faster (at least beyond a reasonable point in the transition zone from being a limiting nutrient to not being limiting). The exact threshold depends both on the species and on the levels of the other nutrients.

In the ocean, the limiting nutrient is iron in some locations, and for different algaespecies, can be either N or P limited in the same location.

Hi Randy, is K a factor here or does that only apply to plants?

Randy Holmes-Farley · Jul 22, 2015

acbaldwin said:
Hi Randy, is K a factor here or does that only apply to plants?

There's actually quite a lot of potassium in seawater, so I don't think it becomes limiting unless it becomes significantly depleted, which is not all that common. I don't think it is ever known to be limiting in the ocean (that I have seen at least).

CastAway · Jul 22, 2015

So if I reduce nutrients to the extent that my nuisance algae and/or desireable macros recede, is it inevitable that I am doing the same to the symbiotic zooxanthella in my SPS?
If I have thriving macro algae but measure little to no PO4, is it simply being consumed as fast as it's produced/introduced making it un-measureable?

Recently I reduced my feeding regime, and saw a noticeable reduction in algae. I was worried for my SPS however and resumed my old schedule, instead focusing on manual removal of the nuisance algae. What is the right direction?