Specific gravity and temperature

[chufa]

Is using a heater to bring the new water up to the same temperature of the tank for specific gravity too much overkill? According to the following, it may as well be.

 

According to an EPA study, pure water expands when warmed 20°F by 0.000966 g/cm³. Therefore, if I understood it correctly, the specific gravity reading you obtain will be lower by approximately 0.001. So, a typical 10 degree difference between the tank water and room temp water would result in a negligible difference (0.00025).

[printerdown01]

LOL, I often wondered how much temp affected SG. But I never really worried about it for two reasons: a) I have never noticed a real difference in SG readings with differnet temps. The SG test kits that we all use for aquariums aren't really that accurate anyway (just keep your SG steady).

[Jefe12234]

I always heat the water before adding salt. I use the chart shown in this article for SG/salinity conversions.

 

http://www.animalnetwork.com/fish2/aqfm/19...s/1/default.asp

 

It shows that SG varies by ~1 point (0.001) for each 6° change in temperature. So for a typical 10° difference, SG would change by ~1.7 points (e.g. 1.025 would become 1.0233 when heated). That's significant enough for me to warrant preheating the water.

 

Maybe your information is incorrect here because it only applies to freshwater. I'm not sure though, I'd have to look into it more.

 

-Chris

[Fant]

Why i use auto temp compensation refractometer.

[LEEWINK]

go with jefe,

 

cheers,

lee

:) :)

[Bocephous]

I heat the water anyways cause I dont want to give my fish hypothermia when I do water change =D

[leslr]

I just use a thermometer and Hydometer to check the temp and SG of the tank before I do my water change/topoffs and then heat my water to the same temp and adjust the SG to the same as the tank readings. Hense, no surprizes like you get from using 2 different thermometers etc.

lelsr.

[MrConclusion]

Actual specific gravity change due to temperature is minor... BUT... hydrometers and other non-compensated SQ meters will only read true at a certain temperature.

 

Most glass hydrometers are calibrated for 60ºF, so you must compensate if reading at a higher or lower temperature. This is not so much due to the SG of the fluid changing with temparature as is is the test device going outside of design parameters.