According to directions published on the internet - in particular, that of
Chris Cow, found at:- http://www.tomgriffin.com/aquamag/cycle2.html, I have
decided that I need to attain a concentration of 5 ppm in my tank of two
cubic feet. I was hoping other people here could review my calculations, and
make suggestions along the way.

I have converted two cubic feet, and it works out at 14.9 gallons, or 56.6
litres. Given that my tank is not full to the brim and contains gravel, for
the ease of calculation, I will say 50 litres.

I have a bottle of 9.5% ammonia, purchased from Boots (UK). It's very
smelly! To make it easier to work out, I'll assume 10% concentration.

In a 100% solution, one ml in one litre is one part per thousand. Divide by
1000 and we have one part per million. So that's 0.001 ml in one litre.

Since we have only a 10% solution, we need 10 times as much. So that's 0.01
ml in one litre.

For fifty litres, that's 0.5 ml to attain a 1 ppm concentration. To work
this up to 5 ppm, that's 2.5 ml.

Anything wrong with my calculations?

Marcus