Derek, everything I said in this forum is I tried before with real experience and not paper talk (reading/heard/saw in internet or elsewhere) like some reefers here.
I done hyposalinity treatment many times and the only reason why yours will fail is that you did not lower the salinity sufficiently. I feel you should use a refactometer which gives a more accurate reading.
I prefer to use the ppt instead, you should keep the sg of the water below 16ppt at all times, 14 ppt is recommend as you have buffer for evaporation.
Also are you checking the salinity of the water daily?If at any point of time the salinity raise above 16ppt then you have to repeat the full period of the hyposalinity treatment again.
Good luck to you, time to invest in a refactrometer.