Iron and Algae

[Morpheosz]

Although by pretty much all measures (extension, growth, alk/ca uptake, etc) my tank inhabitants have been thriving, over the last 2-3 months, I've had a lot of brown/green algae growing primarily on my sand. It never used to happen, in fact my larger chunks of rubble in the sand were turning purple with coralline growth while the rest was largely staying white. My nutrients are as low as they've ever been - NO3 = ~3-4ppm and PO4 = .04ppm and have been stable for quite some time. The one thing I noticed a few weeks ago is my DI resin must have been exhausted and I was reading 1 TDS coming out of the RO filter so I changed the resin. Just for fun, I took a sample of my recently mixed salt water before I changed the resin and sent it off to Triton for an ICP test to see if there was something coming through that could explain and in looking at the results only one thing jumps out at me, Iron. I'm using tropic marin pro salt, curious if anyone knows if this is normal, or if I have some other source. Additionally curious if any hypothesis if this could be contributing to my algae issue?

 

[Randy Holmes-Farley]

Algae use iron, but so do all organisms, and photosynthetic ones likely get it from the water.

Like most limiting elements, iron can be low enough to limit algae growth. It's even true in part of the ocean for phytoplankton. That likely happens at levels well below detection by ICP.

But once you add enough to remove any iron limitation to growth, which again may happen below ICP detectable levels, then more and more does not spur more and more algae because once they get enough, getting more cannot make them grow faster. Something else is then limiting their growth.

Thus, I think it unlikely iron is playing a driving role in this algae issue.

 

[Morpheosz]

Algae use iron, but so do all organisms, and photosynthetic ones likely get it from the water.

Like most limiting elements, iron can be low enough to limit algae growth. It's even true in part of the ocean for phytoplankton. That likely happens at levels well below detection by ICP.

But once you add enough to remove any iron limitation to growth, which again may happen below ICP detectable levels, then more and more does not spur more and more algae because once they get enough, getting more cannot make them grow faster. Something else is then limiting their growth.

Thus, I think it unlikely iron is playing a driving role in this algae issue.

Super helpful, as always, thank you!