Harpic Bloo in cistern blocks foam and you can get lemon ones which don't colour the water if you don’t like blue water BUT if your water is hard, they will foam much less.
Have you ever tried mixing bleach with ammonia gingebee? We used to when were were studying chemistry in our teens. The chlorine gas given off is rather more concentrated than you come across in the atmosphere near a water treatment works. Give it a try sometime but do it outdoors and sniff it VERY carefully.
bhg..I'm well aware of the dangers of chlorine (chemistry degree, chlorine leaks requiring breathing apparatus in water treatment plant etc.)...I was just being mischievous!
Ah, you know more about it than I do then ginge. That's the drawback with discussing things online - you don't know the knowledge level etc of people and can easily misunderstand/misinterpret their posts.