My first question is why are ...

My first question is why are you having ammonia in cooling water?  Is this an ammonia chiller plant?  Ammonia in air around the cooling tower?  Ammonia in source water??

Sodium hypochlorite goes stale (meaning it has its own fugitive emission) so it loses strength, mainly from solar heating of the tank.  Some places install a chiller on the hypochlorite tank to attempt to (mostly unsuccessfully) mitigate the issue.  In my humble opinion sodium hypochlorite use in a large industrial setting is a waste of money.

If your stainless steel is undergoing SCC failure, you installed the wrong metal, sorry, but true.

Chloride dioxide is ideal for cooling tower use, and will provide better control of algal growth at walls and wet/dry areas than any other oxidant program other than "mixed oxidant", although I myself prefer to use chlorine gas with N,N-dibromo sulfamic acid salt.  Mixed oxidant is produced is a specific electrode arrangement using DC (sometimes AC) current, in a high strength sodium chloride brine.

Chlorine dioxide is not nearly as volatile (gaseous nature) as chlorine water solution, so I would not be as concerned with tower losses due to air exchange.

Phosphate in the treatment program is not the limiting factor in algal growth.