Originally Posted by
SCSInet
Well... one could argue that they are in you for the long term investment...that you'll spend a TON with them as you replace dead invert after dead invert due to outa whack SG.
Seriously though... the plastic ones can work well enough, but they can also be very badly inaccurate. If you mix your seawater yourself, a refractometer is a requirement. If you buy seawater and have an LFS that can do a refractometer-backed water test every month or so, a plastic one will suffice. I started with the plastic ones, moved to the glass (then found that the glass ones are really hard to read because the entire range for seawater constitutes about 1/8" on the scale), back to plastic, then to a refractometer. I am still using my first refractometer to this day and it's still dead on accurate.
I went to the the LFS to do a little test, Prior at my house 1.025 and the at the LFS 1.025, exactly the same, so you see it can be accurate, but i heard that after a while the plastic ones get salt creep and and stick AND can slowly become innaccurate, but at that one present moment i WILL give aquarium pharmacuticals thier respect!