Can silicate dosing inhibit calcification?

[Miami Reef]

I think I might be the first person in the reefing community to wonder this.

What’s my reasoning?

Phosphate gets adsorbed on rocks and calcium carbonate.

Phosphate can inhibit calcification.

Silicate can interfere phosphate tests.

Can silicate adsorb onto calcium carbonate surfaces?

I asked, and I got this answer:

I expect it does to some extent, but I’m not sure how much or if it is significant in a reef context. For example, calcium silicate is not very soluble, indicating a good likelihood of some binding.

So, do you think 1-2ppm silicate can inhibit calcification?

 

[Pod_01]

Phosphate can inhibit calcification.

Just curious, is there established threshold where this has been shown to be true in reef tanks?

There is lot of anecdotal evidence or repeated statements that 0.2ppm and above is the threshold but there is also anecdotal evidence that 1ppm is ok…

So far I have not observed any issues with corals and having PO4 at 0.2 - 0.9ppm levels…

Silicate may be the same…

 

[Randy Holmes-Farley]

So, do you think 1-2ppm silicate can inhibit calcification?

I don’t know the answer to that.

 

[Miami Reef]

I don’t know the answer to that.

Thank you for responding, though. Not everyone can admit when they aren’t sure of something. It’s commendable.

Do you know the silica concentration level at which it starts to become limiting for sponge growth?

Also, do you have any studies on hand that shows sponges can directly uptake acetate?

Thanks so much!

 

[Miami Reef]

Just curious, is there established threshold where this has been shown to be true in reef tanks?

There is lot of anecdotal evidence or repeated statements that 0.2ppm and above is the threshold but there is also anecdotal evidence that 1ppm is ok…

So far I have not observed any issues with corals and having PO4 at 0.2 - 0.9ppm levels…

Silicate may be the same…

I’m not sure. I can source some studies, but the consensus seems to be mixed?

I like to follow Randy’s recommended phosphate levels of 0.02-0.10ppm.

 

[taricha]

So, do you think 1-2ppm silicate can inhibit calcification?

If we re-phrase the question as "inhibit calcification - relative to natural seawater" then we can give ourselves an out, and the answer is 'No', because these values are found in/around reef waters.
"Inhibit calcification rate - relative zero SiO2", probably. But then we could ask do you really want zero inhibition to calcification? You could argue that a system with corals overcoming very slight natural sized barriers to calcification might be better than a hypothetical system where there's no calcification barrier and calcification rates (and likely abiotic precipitation rates) are maximally fast.

 

[Miami Reef]

If we re-phrase the question as "inhibit calcification - relative to natural seawater" then we can give ourselves an out, and the answer is 'No', because these values are found in/around reef waters.
"Inhibit calcification rate - relative zero SiO2", probably. But then we could ask do you really want zero inhibition to calcification? You could argue that a system with corals overcoming very slight natural sized barriers to calcification might be better than a hypothetical system where there's no calcification barrier and calcification rates (and likely abiotic precipitation rates) are maximally fast.

Perfect. Thank you very much.

I was wondering what level natural seawater silica was because if it works for the ocean, it works for me. I understand that silica is very variable.

I’m trying to win a growout competition, so I’m just trying to cover all my bases lol

I’m still curious as to what level silica starts to become limiting to sponges and the paper that shows they can consume acetate.

 

[Randy Holmes-Farley]

Silicate varies a lot in the ocean:


The concentration of soluble silica in the ocean is highly variable. In near surface waters, diatoms are very efficient at sucking it out of solution to make their SiO2 frustules. A diatom bloom in the ocean can drive the concentration of silica down from a value not atypical for the whole ocean, 45 uM (2.7 ppm SiO2), to less than 1 uM (0.06 ppm SiO2), at which point the diatoms can become silicon limited. Typical silica concentrations in the surface waters of the equatorial Pacific are a few uM.

Rivers are the primary input of silica into the oceans (80% of the total input; underwater vents and deposition from the atmosphere are also significant contributors), and river water worldwide averages 150 uM (9 ppm SiO2). Consequently, coastal areas near a river may have greater silica concentrations than open ocean areas. This input is approximately balanced by the deposition of silica on the ocean bottom. However, the total biogenic incorporation of silica into organisms is about 40 times as fast as river input, indicating that much of the silicon is deposited into skeletons and re- dissolved many times before it becomes “permanently” incorporated into sea floor sediments. The average residence time for a single silicon atom in the oceans is only about 400 years, before it gets deposited in some fashion.

When diatoms and radiolarians die and sink, they slowly dissolve, and the silica concentration in deep water can be much higher than surface water for this reason. All ocean waters are undersaturated with respect to amorphous silica (allowing the silica structures in diatoms and radiolarians to dissolve), and most waters are undersaturated even with respect to quartz, although its dissolution is kinetically slow, allowing beaches to exist.

 

[taricha]

Do you know the silica concentration level at which it starts to become limiting for sponge growth?

one more thing I'll mention, because I don't see it discussed frequently - there seems to be silicate cycling in a reef tank - meaning some processes release Si and not just growth consuming it.
When I first messed with SiO2 dosing, my tank had essentially none. I dosed SiO2 off and on for a number of months. but now I don't - I haven't added any SiO2 in any comparable way in over a year now - and my SiO2 level is staying ~0.5ppm SiO2. Even though I occasionally get flushes of diatoms growing on glass. SiO2 remains at that level now.
So probably consumers of sponges and diatoms re-cycle some Si back into the water once there is enough Si added and enough biomass of Si-rich organisms that their consumption can re-release some fraction of Si back into the water.

 

[taricha]

and this process can also explain my above observation. Doesn't acually require consumers. can just be dead diatoms/sponges.

All ocean waters are undersaturated with respect to amorphous silica (allowing the silica structures in diatoms and radiolarians to dissolve),

 

[Randy Holmes-Farley]

one more thing I'll mention, because I don't see it discussed frequently - there seems to be silicate cycling in a reef tank - meaning some processes release Si and not just growth consuming it.
When I first messed with SiO2 dosing, my tank had essentially none. I dosed SiO2 off and on for a number of months. but now I don't - I haven't added any SiO2 in any comparable way in over a year now - and my SiO2 level is staying ~0.5ppm SiO2. Even though I occasionally get flushes of diatoms growing on glass. SiO2 remains at that level now.
So probably consumers of sponges and diatoms re-cycle some Si back into the water once there is enough Si added and enough biomass of Si-rich organisms that their consumption can re-release some fraction of Si back into the water.

I’ve also wondered if all Si in reef tanks is silicic acid/silicate, and not some other form that is less bioavailable.

In your case it would need to be detectable by kit, but my question also relates to icp which greatly widens the range of possible chemicals to include silicone materials.