Question re: Specific Gravity of Vinegar

[littlelacho]

This may seem like a strange question but does anyone know the SG of plain old, commercial white distilled vinegar? The reason I ask is I have been using an Instant Ocean swing arm since set up and some of my corals are not looking happy recently...my mushrooms are shrunken up, my cloves are spreading but have lost their feathery look and I now have zoa pox on two frags. So I bought a glass hydrometer as I was told they are more accurate. I will be getting a refractomer in the next two weeks or so. Well, my swing arm was reading 1.026, where I have been holding it steady and the glass hydrometer said 1.020!! So I have slowly, starting with my most recent water change on Friday and top offs, brought the SG up to 1.026 by the glass hydrometer's reading. This morning, my glass hydrometer is reading 1.020 again! This obviously can not be true so my thought was, until I can get to the LFS this weekend that does use a refractometer (the one I went to this past weekend uses a swing arm so didn't bother having them test it) and get a true reading, I can test a liquid with a known SG to know how far I am off. I rinse my swing arm after every use but there have still been salt deposits in it so I got vinegar to let it soak overnight. If I knew the SG of the vinegar, that would help me know how far off my hydrometers are to see how far off my tank SG is until I can get it tested by refractometer. I found conflicting numbers online.

 

Anyone know? I know we have some really educated people here

[Amphiprion1]

http://www.engineeringtoolbox.com/specific...uids-d_294.html

 

You'd be looking at the 5% value there. Keep in mind that while the percentage is consistent, the SG will vary slightly. Not only that, but if the slope of any of the devices is miscalibrated, then calibrating it at the lower end like that will lead to a larger error when trying to extrapolate to seawater salinities.

[littlelacho]

Thank you for your response. I did see this link, and was confused as the bottom has vinegar listed at 1.008 and didn't realize what one I should use. Is there a better way to determine how far off my swing arm is reading? I am worried that the glass hydrometer is reading incorrectly as well and have no idea what my SG is until I have it checked with a refractometer. I only thought of the vinegar since I was soaking the hydrometer in it. Do you know of a better way for me to accomplish this in the interium?

 

Thank you again for your help!

[Amphiprion1]

5% acetic acid is standard household vinegar. The link lists it at 1.006 @ 59 F. You'll need to get a temp/SG table and convert that to a more standard room temp. It will be even less than 1.006 when it has warmed up. That, again, is pretty variable up to 1.01. That's enough that I wouldn't use it as any sort of standard. You need a seawater standard. Take a look at this link:

 

http://reefkeeping.com/issues/2004-06/rhf/index.php

 

Just use accurate means of measurement, not the 2L bottle.

[littlelacho]

Thank you very much. I agree and will read this article. I appreciate it