Sodium Silicate effect on zoas?

elysics · Sep 9, 2020

So, i have been daily dosing sodium silicate for a long while now. I initially mixed up a solution that i calculated to raise the tank level of silicates by 1ppm with an addition of 3ml. Currently i dose 5ml of that per day.

I dont know if i just didnt notice it before or whether it started recently, but for a month now i am seeing a pattern: I manually dose the whole dose of the day in the morning by adding it dripwise into a surface skimmer in batches over an hour or so. With a delay of a few seconds (which should align with the speed of the moving water) after adding the first batch, around 1ml or so, which should be +0.33ppm silicates in the whole tank, i notice that my flame scallop and the zoas getting the most flow, quickly react by closing up. Other inhabitants (zoas with less flow, one zoa sitting between the main two that are affected, SPS, LPS) seem to not react visibly.

What could this be? Does that "small" dose already have a considerable effect on tank PH? Did i maybe get a concentration gradient in the sodium silicate solution and i am dosing more than i think? Is dosing it directly into the intake of an eheim skim350 not enough to chop it up and dilute it?

Randy Holmes-Farley · Sep 9, 2020

The reaction you see is likely due to not having the solution mixed in well before it gets to them, and the local pH will be high where it is added. Salinity is also high right were it is added, but that drops pretty fast as it mixes in.

I don't think they know or care about silicate itself.

elysics · Sep 9, 2020

Im not sure i can have it mix in any more, it goes through the skim350, probably half of it through another powerhead, and then through half the tank before it gets to the zoas. And that's with dropwise addition. I could dilute it much more i guess.

Do you have any experience with using a dosing pump for silicates? Based on the state of the syringe i use when i don't flush it afterwards i don't think a dosing line would last long, particularly if i dose dropwise and it dries a little bit inbetween.

elysics · Sep 17, 2020

Mixed up a new solution with the same initial strength (around 33 grams of 36% sodium silicate solution in 0.5l RO/DI) and the reaction is almost gone, one zoa still reacts but goes back to normal in a matter of a minute rather than staying closed a long while as before.

Seems like the last 50ml or so in the last batch where much more concentrated, does this stuff have a tendency to unmix? Ill try and shake it up everytime before dosing now and see if the issue comes back again.

Randy Holmes-Farley · Sep 17, 2020

elysics said:
Mixed up a new solution with the same initial strength (around 33 grams of 36% sodium silicate solution in 0.5l RO/DI) and the reaction is almost gone, one zoa still reacts but goes back to normal in a matter of a minute rather than staying closed a long while as before.

Seems like the last 50ml or so in the last batch where much more concentrated, does this stuff have a tendency to unmix? Ill try and shake it up everytime before dosing now and see if the issue comes back again.

It might have concentrated by evaporation, or perhaps you had solid undissolved material in it. That could easily irritate organisms.