if you do hypo, do not do copper as well. The combination could kill your fish.
From what I've read, copper only works in very specific concentrations. Too little, it will have no effect, too much and you will kill the fish too.
I think hypo-salinity is far more forgiving. However, it has no effect on marine velvet which it doesn't sound like what you have. Couldn't hurt to double check.
I installed a float valve on mine to keep the salinity constant. I did water changes virtually every day or other day to keep down ammonia/nitrites/nitrates. It's a royal pain in the butt... If you want to make it easy, add a bulkhead to the tote around the middle so you can do an easy 50% water change and have it drain to some place. And place it such that you can fill it easy. You don't want to make it hard to keep this routine up because 4 weeks is a long time.