Sodium Metasilicate Unit Conversion For Culturing Diatoms...?

VBMike · May 10, 2015

Hi Mr. Holmes-Farley! I don't post a lot, but I enjoy reading your posts and articles.

I don't know how familiar you are with culturing phytoplankton and diatoms, but you need silicates to grow diatoms. Sodium metasilicate is a commonly used source.

My question isn't about culturing diatoms, but how I can convert the measurement of this stuff to the recipe I have for sodium metasilicate. Or if there's even enough information to do the conversion.

I bought some stuff on clearance called "SpongExcel" by Brightwell. I grabbed it because the ingredients are listed as "Purified water, Sodium metasilicate". The guaranteed analysis states "Silica (min) 15,140 ppm". It contains 125ml.

My recipe states that I create a stock solution of 9 grams sodium metasilicate to 300ml of water, then I use 2ml of this solution per 1 liter of culture.

So... how much SpongExcel do I use per liter of culture? :tongue:

Thsnks!!

Randy Holmes-Farley · May 10, 2015

Welcome to Reef2Reef!

For most purposes, the terms sodium silicate and sodium metasilicate are used relatively interchangeably. Sodium silicate solution is a complicated beast, but is probably best characterized as Na2SiO3 in water.

I dose sodium silicate solution to my aquarium to promote sponges and diatoms using a cheap sodium silicate solution, and that is presumably what they use for the Brightwell product (although I cannot be sure).

9 grams of dry sodium metasilicate contains 0.074 moles of SiO2, or 4.4 grams of SiO2.

Assuming Brightwell is correct with their numbers (and for some reason they are not always accurate on their web site), 4.4 grams is contained in 4.4/15.14 = 0.29 L or 290 mL of their product. So it looks nearly the same as what you are already dosing.