salinity levels requested

Kevin, you don't think the swing-arm type are consistantly off. i.e. that they couldn't just be compared to a refractometer to get a constant difference that is either added or subtracted from the swing-arm reading even at a different salinity?

I have looked all over for a floating hydrometer with a lot of space between the graduations. All that I've seen have about 1/4 - 1/2 inch between 1.020 and 1.030. Is your's wider then that?

Floating hydrometers can be very accurate. I won't vouch for the ones sold in fish shops, but we have/use many different sized ones out at work. The largest (at least most popular) manufacture of precision hydrometers is Ertco. If you're using a lab standard hydrometer it's most likely an Ertco and calibrated to 60°F so you must adjust your reading to your tank's temperature. Most that I've seen sold in pet stores are calibrated to 77°F and there is a very slight adjustment from there to say 82°F (may not be worth the bother).

Thanks Kevin, I'll look for the Tropic Marin (did you find it locally?).