I ordered it from My Reef Creations(great deal BTW). My hydrometer was reading the specific gravity at .023. When I used the refractometer it shows a specific gravity of .027! Wow a huge difference. At first I thought, "Man this thing is way off". But then I realized that it's my hydrometer that has prolly been off all along. I slowly have brought the SG to .025 per the refractometer. What do you guys think? Is there much of a margin of error w/ the refractometer, surely it is more accurate than the hydrometer? Thoughts?