Well, my intention was not to "put the fear of god" in him, but merely to warn against a potential disaster. I wouldn't want to go through the process of hooking everything up just to nuke my fish! I was just sharing my point of view on it, just like everyone else. My experience has been purely negative with previously used pool filters. I do know others who have used new pool filters and they have worked fine, at least in the short term. Wouldn't you rather be cautious than ignorant?
As far as residual chlorine, much of it can actually permeate the plastic in the filter over time and create problems. I'm glad you took the time to calculate ppm, but the fact is that if someone told me to be careful when trying something with my fish tank - I WOULD BE CAREFUL. That's all.