I used the following calculation to work out how much to put in. (depends on the % solution of your ammonia)
so.. 5ppm
if 1 litre is 1000 ml, then 1000 litres is 1 million ml...
then 5ml of pure ammonia is 5 ppm in that soltion..
so
100,000 ml of water would require 0.5 ml ammonia
10,000 ml of water (ten litres) would require 0.05ml of ammonia
the solution is only about 10% ammonia, so that would need 0.5ml of my solution (in fact it was the homebase one.. but i rounded it up)
so i tested this in a bucket and it went green (somewhere over 4ppm, but not entirely sure as the kit is not that clear over 4ppm)
so..
my 180 litre tank would require 18 * 0.5 =9ml of my solution..
Hope that helps, but as you can see, it depends on your ammonia solution. I also used a syringe to get the ml right instead of drops, so it depends on how many of your drops there are to a ml. You can get a small syringe from a chemist.. or use one of those medicine things or a small measure (be careful if people are using it for medicine still
might no be the right thing to do there).. lol
Cheers
Squid