Hang on, if you have an alkaline solution (bleach) and you add an acid to it, don’t you just end up with a weaker acid or a weaker bleach and perhaps some fizziness?
not quite as simple as that – but if you get it wrong “some fizziness” is actually going to be chlorine gas – uses in WWI as a chemical weapon, and the result of many a swimming pool evacuation over the years when someone, with some training and test kits at their disposal, gets it wrong…