That's with my 3gpd pump. I could turn my 3gpd pump wide open and it wouldn't hurt anything. But other people may have much larger pumps and it could inject a fair amount of bleach into the line.
It won't matter if you stop the flow to the returns as long as the flow is going out the waterfall. Unless, you have one of those high rate injection pumps that could possibly raise the FC fairly high.
Most of the time this isn't going to be an issue. It's only those cases where someone is injecting a whole days chlorine in a minute or two. And even then, it's probably not a problem, but people need to be aware of what could happen.
It won't matter if you stop the flow to the returns as long as the flow is going out the waterfall. Unless, you have one of those high rate injection pumps that could possibly raise the FC fairly high.
Most of the time this isn't going to be an issue. It's only those cases where someone is injecting a whole days chlorine in a minute or two. And even then, it's probably not a problem, but people need to be aware of what could happen.