how far can you drop salinity?

how far can you drop salinity in a fish and live rock only tank? got ick at the min

 

Some publications state 1.015. However, I have read articles that detail dropping the SG to 1.008 to 1.009 and keeping it there for a month after the last spot has disappeared. You must do it slowly though. A good rule of thumb is dropping it by no more than 0.02 per 24 hours, although I think you could push the outer envelope on that a bit.

 

I quarantine all fish at 1.0075 for at least 6 weeks and usually two months min.. (you have to be dead certain of your readings to go this low)
I have had even one fish still carrying at that point, my achilles tang, which I eventually had to copper to stop the ich.
I believe it is due to strains that have evolved to be able to live under these extreme conditions and while they may not always be present, for me, it wasn't worth while to have to redo a treatment at a low s.g. after failure at a slightly higher reading.