OK, the Aquarium Calculator is still bust, so we'll have to do this the old fassioned way; With Mathematics

(Disclaimer, I failed AS-Level maths, so it would be advisable to check my working before trying to use it

)
You are targeting ammonia levels of arround 5ppm, or parts per million, or 5/1000000 of a liter in the tank being pure ammonia. So, assuming you have 100% ammonia in that bottle (Which you don't) you work out the following.
55l * 5 / 1,000,000, which equals 0.000275l of pure ammonia required.
Homebase ammonia is usualy 9.5%, so you need to accomodate this, by doing the following;
0.000275/9.5 * 100 = 0.0026l of ammonia required, or 2.6ml
Some ammonia will evaporate out of the solution, so this may come in a bit low. Start with that and test to see if it's ok. Add more if required
A quick check says that should be right. I needed 16ml for 335l, so a check would be to do the following;
16/335 = 0.477... * 55 = 2.63...ml required
All the best
Rabbut