Specific gravity, salinity, and temperature

[pro2k]

I have a question about the salinity reading of my reef tank. I think most people keep a salinity of about 32ppt or a density of 1.024. My question is since the density varies with temperature do you have to make a correction to the observed hydrometer readings?? What I'm saying is if my hydrometer says 1.024 and the temp is 76F is that really a salinty of 32ppt? (are the hydrometer calibrated for a temp around 76?)

[leebca]

Each hydrometer is usually calibrated to a specific temperature. You have to check the supplier and/or manufacturer of your hydrometer to determine at what temperature it was calibrated to. The supplier/manufacturer should be able to point you to a table for making corrections on the salinity reading for the temperature.

[romunov]

I would suggest you get a refractometer.
You take a drop or two of water, put it on the glass, cover it, look through the instrument and that's that. No splash, no mess. :)

You will find that getting compensation tables isn't as simple as one would think.

You can see www.advancedaquarist.com for some more info. Randy wrote an article about this once.

[silkchaos]

Actually, just do a search on "brewing" and specific gravity to find a table. As a brewer, I use a table when I make wine & beer to check the sugar content.

One table on line:
http://www.howtobrew.com/appendices/appendixA.html

Robinson

[bertoni]

http://reefkeeping.com/issues/2004-06/rhf/index.htm
http://reefkeeping.com/issues/2004-07/rhf/index.htm

I second the refractometer idea, especially if you're using a swing-arm. A conductivity meter, like the PinPoint salinity monitor, can work well, too.

[leebca]

Some are jumping too far ahead regarding the refractometer.

Who here knows the size of pro2k's aquarium? how much he's into the hobby? Would you recommend someone buy a refractometer and meters who owns a nano cube? The hobby is expensive enough as it is. At least find out how large the reef tank is and how much into the hobby the person is and just how accurate they need to be, before recommending expensive equipment those of us need for our level of involvement.

Just my opinion guys. :D

One of my earlier mistakes as a shop owner was to recommend to a guy to get a refractometer. Then he told me in our conversation his tank was 15 gallons. I told him to forget the refractometer. At that time the refractometer cost more than his aquarium setup!

[tptram]

i think stability is more important
i have both the refractometer and hydrometer

i pre-heated the water to match the tank temp and use the hydrometer to match the SG to tank's water.

for example,
i keep my tanks @ 81 and according to the hydrometer it is 1.022 SG
when it is time for water change, i would heat the fresh water to 81 and mix in salt until the hydrometer is at 1.022
if i use my refractometer to check, it would show 1.024.
so my hydrometer definitely not calibrate @ 81 degree :)

as long as the water change does not make salinity level fluctuate then i think it is good.

and i use the hydrometer more often than my refractometer ;)
once in a while i would calibrate the hydrometer against the refractormeter
and calibrate the refractometer with distilled water and a friend's

i always has about 30 gallons of pre-mixed water on hand. and when it is time for water change i only add a bit more fresh water or salt to match to tank water.

[bertoni]

I keep a 12g tank, and quite frankly I'd spend the money on a refractometer for that one tank. At $40, it's a bargain IMO. Yep, I'd recommend a refractometer for a nano-cube. The long-term cost in this hobby is the electricity in my computations.

[Benny Z]

Originally posted by tptram
i think stability is more important
i have both the refractometer and hydrometer

i pre-heated the water to match the tank temp and use the hydrometer to match the SG to tank's water.

for example,
i keep my tanks @ 81 and according to the hydrometer it is 1.022 SG
when it is time for water change, i would heat the fresh water to 81 and mix in salt until the hydrometer is at 1.022
if i use my refractometer to check, it would show 1.024.
so my hydrometer definitely not calibrate @ 81 degree :)

as long as the water change does not make salinity level fluctuate then i think it is good.

and i use the hydrometer more often than my refractometer ;)
once in a while i would calibrate the hydrometer against the refractormeter
and calibrate the refractometer with distilled water and a friend's

i always has about 30 gallons of pre-mixed water on hand. and when it is time for water change i only add a bit more fresh water or salt to match to tank water.

i like the way you do this! i'll have to follow this plan when i get a refractometer.

that said...i have 1 concern after reading your post...

i keep my temp at 80* and use a swing-arm. i measure in at 1.025 and a half. according to your temp correction for 81*, i'm now fearing my own specific gravity is too high. what brand hydrometer are you using? mine is the standard aquarium systems brand.

??? :confused:

[tptram]

mine is also aquarium system
i betcha if i compare mine to yours it will be different :)
i don't think your sg is too high (now, that being said only for FOWLR tank)
but if it make you sleep better, you can reduce it a bit.
as long as you keep your sg consistent.
auto top-off is helping immensely

be aware that some lfs keep their fish at a low sg level
one of my lfs keeps @ 1.015
it makes acclimating new stock harder

for invertebrate, a salinity level of 34~36 ppt is preferable
this is when you need a refractometer.
if your fish come down with ich and you want to treat them via hyposalinity then a refractometer is a must.

i think a refractometer is a well spent investment.
--and i use my hydrometer more often :)

HTH