Where does the silicon go?

[s_tempest]

Maybe it’s because I’m cycling a new tank and am in midst of the brown uglies, but I’m thinking about silicates in reef tanks.
So we start a tank and there’s this pool of dissolved silica that diatoms exploit and bloom. Result - the brown uglies that soon go away.
But go away ... where?
The tank is a (largely) closed system. There could be some export via sand-bed vacuuming, maybe via a skimmer. But even if those are not active, the diatom bloom goes away. Why?
Where is the silica after the bloom? Is there some low sustained diatom population for the life of the tank? Is the Si forever internally recycled?

 

[Hemmdog]

I’m guessing it turns into the shells of what feeds on the diatoms: pods, clean up crew, etc.

Sand bed vacuuming for sure as well.

 

[s_tempest]

I’m guessing it turns into the shells of what feeds on the diatoms: pods, clean up crew, etc.

Sand bed vacuuming for sure as well.

Maybe, but their shells/tests are mostly chitin or CaCO3. I wouldn’t think that’s much Si export. And do those shells lock it away permanently or do they get degraded?
This is something I’m loving about keeping aquariums: professionally (academically) I’ve been a Biogeochemist for over 20 years, but this hobby makes me find new questions every day.

 

[Hemmdog]

Maybe, but their shells/tests are mostly chitin or CaCO3. I wouldn’t think that’s much Si export. And do those shells lock it away permanently or do they get degraded?
This is something I’m loving about keeping aquariums: professionally (academically) I’ve been a Biogeochemist for over 20 years, but this hobby makes me find new questions every day.

I love the scientific questions in this hobby too I’m not sure on this one. You make some valid points. Following along though

 

[little_sardines]

I know some sponges soak up silicates, perhaps they get consumed by the beginnings of the sponges that grow in the low light spots in a lot of our tanks?

 

[vetteguy53081]

Sponges and other media absorb it but at low levels

 

[Dan_P]

Maybe it’s because I’m cycling a new tank and am in midst of the brown uglies, but I’m thinking about silicates in reef tanks.
So we start a tank and there’s this pool of dissolved silica that diatoms exploit and bloom. Result - the brown uglies that soon go away.
But go away ... where?
The tank is a (largely) closed system. There could be some export via sand-bed vacuuming, maybe via a skimmer. But even if those are not active, the diatom bloom goes away. Why?
Where is the silica after the bloom? Is there some low sustained diatom population for the life of the tank? Is the Si forever internally recycled?

I had the same question when I measured silicate level (Hanna Checker) in my fish only aquarium after dosing sodium metasilicate. Where does it go? And why so quickly? I am looking into the possibility that a portion of it binds to aragonite but does not desorb like phosphate.

In new aquaria, silicates probably start out high and decline over time, though I am not aware of anyone that monitored silicate level during the first year of an aquarium’s existence.

 

[s_tempest]

I had the same question when I measured silicate level (Hanna Checker) in my fish only aquarium after dosing sodium metasilicate. Where does it go? And why so quickly? I am looking into the possibility that a portion of it binds to aragonite but does not desorb like phosphate.

In new aquaria, silicates probably start out high and decline over time, though I am not aware of anyone that monitored silicate level during the first year of an aquarium’s existence.

I think I’ll do a search thru some aqueous geochemistry journals. It’s hard to see that the silica tetrahedra could substitute for the planar carbonate. But maybe someone has worked on adsorption of silica onto aragonite.

 

[Dan_P]

I think I’ll do a search thru some aqueous geochemistry journals. It’s hard to see that the silica tetrahedra could substitute for the planar carbonate. But maybe someone has worked on adsorption of silica onto aragonite.

I have been doing some reading, and nominate the precipitation of magnesium silicate as an abiotic mechanism for silicate removal in saltwater aquaria.

I am on my third silica dosing experiment. The first two had identical zero order rate constants.