Temperature correction on a hydrometer for 48F tank?

[jennm]

Here's one for you...

I have a customer who maintains the live lobster tank at a supermarket. They are provided salt mix that's for use with food fish/crustaceans, and she's trying to sort out the the tank, there was a problem with it in her absence when she went on vacation recently.

I encouraged her to buy a refractometer, but that didn't fly so she bought a hydrometer (cheaper)... Refractometers can compensate for temperature, but hydrometers don't.

Now we are trying to figure out the specific gravity of the tank, factoring in the temperature, which is 48 degrees Fahrenheit.

I've googled around and I cannot find a conversion chart that goes that low.

Can anybody point me in the right direction?

Jenn

 

[weaglereefer]

This help?

 

[jennm]

Sorta kinda but not really

She's got a reading of 1.021 on her swing arm hydrometer. I was thinking that those are calibrated to a temperature of around 60 F but that may only apply to standard (ie floating) hydrometers)....

In my search to find what temperature they are calibrated to I found this:

http://reefkeeping.com/issues/2004-07/rhf/index.php">http://reefkeeping.com/issues/2004-07/rhf/index.php</a>

RHF says that the swing arms don't need to be temperature-corrected... so that may have just answered my question...

I know that most refractometers compensate for temperature, but I thought that hydrometers didn't, and as such, I'd have to calculate what the hydrometer reading was, versus the *actual* specific gravity.

Perhaps not... unless there's conflicting info out there (and there probably is!)

Jenn

 

[coolsurf]

You may find this helpful as well....

 

[weaglereefer]

coolsurf;540882 wrote: You may find this helpful as well....http://www.aquatext.com/tables/hyd9-18.htm">http://www.aquatext.com/tables/hyd9-18.htm</a>[/QUOTE]


That looks more helpful, and it looks like you'd be shooting for 26ppt

 

[jennm]

Yes. I think she said the instructions on her salt pack said aim for Salinity of 22-25 PPT. I haven't seen the instructions, she came in to buy the hydrometer, and called me to help interpret the reading she got.

Looking at that chart, that would make sense.... I think... I believe 48F is about 8.8 C so I looked at the chart for 9C (close enough!) That would be 1.017-1.021 on the hydrometer, and she got an initial reading of 1.016, but not all the salt was dissolved yet.

My head is swimming now

Jenn

 

[misu]

why not warm up a sample and then test it?

 

[jennm]

I suggested that but she was sort of in a hurry...

This isn't a hobbyist we're dealing with - it's a person working in the seafood department at a busy supermarket :-/

I still think she'd have been better off with a refractometer but the store wouldn't approve a $50 instrument. Seems weird to me considering the cost of the livestock they keep in the tanks. I don't eat lobster (allergic) but I think it's pretty expensive...

Jenn