Follow GREECH's advice, He has given me alot of advice since I have joined this forum
I am pretty new to the salt water tanks, and I am going by how I have my tanks set up. I have corals and fish, so I follow the guidelines on the bucket.
as for the Hydrometer,
My experiences so far.... I have purchased two, calibrated as directed using ro water, both meters gave different readings compared to the refractometer. All were with in range, but the refractometer is much more reliable IMO. I seen the same water on the low end and high end of the scale using the same hydrometer, the refractometer was consistant.
this is an example of personal prefrence... with me being a newbie at this, I want to make sure I am doing it right, so the extra money is worth the piece of mind.