I have a 75gal.FOWLR it is well established 6 -7years old . My question is will hypo-salinity kill snails?other websites say it will also how long do I need to treat?Some websites say 2weeks after the last white spots are seen on the fish while others say 4weeks and some go as little as 1week. Does anybody know what the correct time is? I only want to do this once