although the stoichiometric ...

although the stoichiometric ratio is 1:7, it is always recommended to go above this to say 1:10 (we found this adequate in another application).  However you may also want to consider an alternative for ammonia reduction such as the natural zeolite - clinoptilolite which is able to reduce ammonia to acceptable levels through an ion exchange/adsorption process.  When you ammonia is as high as 7 ppm, you will require high chlorine doses which could be costly.