You know there is an equation you can use for the ppm.
Avagadros constant states each mol of element/molecule/compound contains exactly 6.14x10^23 particles (ppm's, or in this case pptttt trillion trillion trillion etc etc)
1 litre of water is exactly 1 mol.
so if you have an 180 litre tank, it is 6.14x10^23x180 particles inside it, if we then divide this number by 1 million (In effect making this number a 1% part)
Then x by 5-6 and you get the particles you need.
Then you find out the % it is of avagadros constant, and then you find the mol amount from that
Once you find out the mol amount, find the relative molecular mass for ammonia, and find out how much weight ammonia is at that mol amount, and thats how much you have to add
One confusing bit is the division of the 1 million part
If i have 1 million molecules, and i want 10 ppm, then if i divide by 1 million, i get 1 ppm, x by 10, i get 10ppm
Easy, it works with bigger, smaller and numbers that dont end in simple 000000
Most of you are probably thinking "this isnt the easy way"
But meh...I've been doing them kind of calculations for years now so all it takes is 40 seconds.
If anyone wishes me to work out for them on a new tank (with no fish) i guarantee my maths will work the same as the bucket method, if it doesnt, simply water change, and i was wrong (though i shouldnt be...the maths makes sense...)