A comment on hanna Silica tester hi705, Brightwell SpongExcel Silica, and measurements & targets
We want to compare the amount of Silica to the amount of Nitrogen and get something approaching 1:1 ratio of Si to N, to follow example of the paper.
N we measure as NO3 so multiply NO3 by 0.226 to get Nitrogen.
I'm going to target 5ppm NO3 = 1.13ppm N, and an equal amount ~ 1.2ppm Si
SpongExcel gives its concentration in terms of Si - great: 1 drop = 0.20ppm Si per gallon (1ml = 4ppm Si per gal)
so target concentration * gallons / 0.20 = # of drops ... (target conc * gallons/4 = # of mL)
1.2 ppm Si * 70 gal / 4mL = 21 mL (420 drops)
This is just to see the total scale of the Si addition - not that you'd add it all at once. I've been dosing a couple of weeks up to now adding 20+ drops a day and increasing 10% a day.
The hanna silica meter measures SiO2 so multiply the reading by 0.467 to get Silicon for direct comparison.
My tank tested at 0.34 SiO2 = 0.159ppm Si
After addition of 22 drops *0.20 / 70 gal = +0.063ppm Si the new level should = 0.222ppm Si
2 hours later the tester gave 0.52 SiO2 = 0.243ppm Si. Considering the uncertainties in measuring drops, my volume, and the meter - this is a pretty confidence-building result.
Overall takeaways:
Si meter and source are reliable.
Even at my very small doses, I'm accumulating some measurable Si.
My tank is consuming Si, but slower than would be expected.
Tank is growing diatoms, and seems to be growing more diversity of them.
It's not really possible to say if the increasing diversity of observed diatoms is due to increasing concentration of Si or simply length of time with available Si.
The "explosion" of diatom growth was very short lived (like 1-2 days) they are now very stable or gradually increasing.
Other things besides Si, P, and N are likely limiting diatom growth to some extent. This maybe should be expected in stable older tanks - tanks don't undergo exponential phase growth of anything for very long before a plateau.
My inverts seem to be fine with new diatoms on the diet. They seem to graze the areas with most diatom growth.
Copepod population on the glass may have increased slightly.
I'll continue slowly ramping up to 1.2 ppm Si to match 1 to 1 the Si to N at 5 ppm No3, and see how the system behaves.
Edit: I don't have a dinos so my observations will be about generally how a system behaves at sustained ~1ppm Si balanced with N.
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