What a load of rubbish, never heard any thing quite so stupid in my life.
We should make a list. One of my personal ones is the lfs's that tell people that their water tests are fine. I think I'll make a color card that starts with really fine, and goes on to pretty fine, fine, almost fine, could be finer, not really fine, far from fine, and nowhere near close to fine.
When I'm filling tanks with the hose, wide open gives me about 7 gpm. I have dumped full 5 gallon buckets into tanks in under two seconds. Neither has caused a problem.
Soliquid; Find another shop, keep going to this shop for advice, but don't listen to a word of it. Post it here, I got a good laugh.