Would also check on ph levels in fw dip. May need to use buffer to keep it in-line with the sw. It might be just me, but I feel folks miss this point too often. I lost a pbt to a few dip without checking ph - with temp being almost the same. Used rodi water.
In many parts of the country, it is actually best to just use tap water and adjust to the proper temperature. The chlorine isn't high enough to cause harm in the five minutes the dip takes, the pH of most municipal water systems runs 7.8 to 8.5. The fact that the water is essentially sterile is a big plus. If you use RO/DI you will have to buffer it. Remember, if you make the dip water too inviting, the parasites won't want to leave the fish(grin). Indeed, Neobenedenia flukes often need a bit of agitation to get them to let go...
Jay