e55MD,here goes,
I also bought into the theory of hypo in the past.However,i tried the hypo routine on 3 different fish,a PBT,a singapore angel and lastly a white-faced butterfly,which by the way broke my heart when i did not make it through hypo.
Ist problem

h instabiliaty.Trying to maintain a 8.0ph is difficult enough with proper salt water.When you lower the salinity,with fresh water,you lower the PH.Then we try and bring the PH up with additives( take your pick of products),and the PH shots through the roof.OH crap!.Lets bring it back down!You see where i am going?Up,down,Up,down.
2nd issue:Ick surviving through the hypo treatment.I lowered the salinity to the prescibed 1.009 with the singapore angel,while all the time fighting the PH issue.This fish ate Formula Two and shaved mussell the whole ordeal!.After 3 weeks,i SLOWLY brought the salinty back up over 5 days,as i recall.At about 1.021,white spots reappeared!Lets not even think about velvet,which is much tougher than ick to kill off.Did not make it through the attempt to relower the salinity a second time.
I am not the only one who has seen this happen.
3rd issue:Nature designed saltwater fish to live in salt water.We are not talking about mollies or scats here,We are dealing with reef dwelling animals,who recieve a benefit from ocean water.To subject them to unnatural water conditions is suspect.Both the PBT and the white-faced buttrefly stopped eating for me when the salinity in my QT hit 1.014,or there abouts.Who knows what kind of damage was done to internal organs,or,digestion,respiration.?.
So,l can only say,copper is the only sure way,IMHO,to ensure that you do not come home one evening to find that prized fish in your reef tank covered in white spots,or the dreaded yellowish sheen of velvet.Copper treatment is a serious endeavor,not to be taken lightly( and i have been quilty of that,believe me).It takes attention to detail,lots of laobor, and the desire to keep that special fish for many years down the road.Sorry for the rambling on and on.I think this is the longest post of my short 5 years stint of being on RC.Think i will go grap a beer.