I think standard CSM+B solution is 1 tBsp per 500 ml H20 to form solution, then dosing at rate of 5ml per 20g of water when running high light and Co2, per Ei recommended starting points.
Now, is your 3g nano high light and high Co2? If not, then you should dose perhaps 50% Ei.
I mix a standard CSM+B solution (1 tBsp per 500 ml H20). I then use this solution to dose all my tanks. For my nanos (using 2x Excel as carbon source) I dose .2 ml per gallon of water (4 drops), which is a little more than the math tells me to. Math tells me to dose around .125 ml per gallon of water (2.5 drops) but I get better results with .2ml and still see no algae. It keeps everything a little greener also.
Now, for your 125 ml bottle you could mix a standard solution by adding 1/4 tBsp (3/4 tsp) CSM+B to 125 ml H20. You could then dose the same amounts I'm dosing. Or, you could perhaps double the amount of CSM+B and then cut your dosage size in half, which would make the 125 ml bottle last twice as long. This of course assumes that much dry CSM+B would completely dissolve into that amount of water. I've never tried anything other than the standard solution.
But anyway, there's your answer for a standard solution and an example of how trying to mix a more concentrated solution might make the small bottle last longer, assuming the concentrated solution would actually mix.
Now, plot a course for healthy plant growth Mr. Badren. .........ENGAGE.
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