I use 50-60ml all the time without trouble. It raises Cl- by maybe 2-3ppm in a week. I use this much because bad handling practices happen, and I mix my batches for others who may not have much of a grasp of planted tanks or that contamination is a problem.
Tom, I think the 5 minute wait is what I was missing. I was having some very fun issues with chelates when HCl was added first.