specific gravity, can it be calculated when combining volumes?

beaniebeagle · 03/12/2006, 10:22 PM

pardon me for my forgetfulness, but that chemistry minor in college was 16 years ago

is specific gravity like combining concentrations (ie the final concentration is the average of the two )???? or is it more difficult like a logarithmic scale...(ie like pH)?

for example, if 10 gallons from my RO/DI with sg=1.000 (when the top off malfunctions) is combined with 120 gallons of sg=1.026---->does it make the sg=1.024

[(120 *0.026)+(130*0.000)]/130=1.024

trying to design a safe guard for an automatic top off (just in case a float valve malfunctions), dont have anything yet

i know solenoids close when they malfunction..but i am trying to design something that doesnt require any power

speakerguy · 03/13/2006, 12:04 AM

Do it using salinity (ie use 35ppt instead of SG=1.026) and it will work perfectly. SG is slightly nonlinear with regard to actual concentration IIRC. But honestly I think the difference is very small in this range.

Randy has an equation that will work exactly for specific gravity I think.

Randy Holmes-Farley · 03/13/2006, 06:01 AM

For specific gravity it will be close enough to being true for our purposes.

trying to design a safe guard for an automatic top off (just in case a float valve malfunctions), dont have anything yet

Using a pump that is only a little bit faster than the demand can be a good precaution, along with a float switch.

03/12/2006, 10:22 PM	#1
beaniebeagle Registered Member Join Date: Feb 2006 Location: baltimore md Posts: 387	specific gravity, can it be calculated when combining volumes? pardon me for my forgetfulness, but that chemistry minor in college was 16 years ago is specific gravity like combining concentrations (ie the final concentration is the average of the two )???? or is it more difficult like a logarithmic scale...(ie like pH)? for example, if 10 gallons from my RO/DI with sg=1.000 (when the top off malfunctions) is combined with 120 gallons of sg=1.026---->does it make the sg=1.024 [(120 0.026)+(1300.000)]/130=1.024 trying to design a safe guard for an automatic top off (just in case a float valve malfunctions), dont have anything yet i know solenoids close when they malfunction..but i am trying to design something that doesnt require any power

03/13/2006, 06:01 AM	#3
Randy Holmes-Farley Reef Chemist Join Date: Apr 2001 Location: Arlington, Massachusetts Posts: 86,233	For specific gravity it will be close enough to being true for our purposes. trying to design a safe guard for an automatic top off (just in case a float valve malfunctions), dont have anything yet Using a pump that is only a little bit faster than the demand can be a good precaution, along with a float switch. __________________ Randy Holmes-Farley Current Tank Info: 120 mixed reef

03/13/2006, 12:04 AM	#2
speakerguy Premium Member Join Date: Aug 2003 Posts: 221	Do it using salinity (ie use 35ppt instead of SG=1.026) and it will work perfectly. SG is slightly nonlinear with regard to actual concentration IIRC. But honestly I think the difference is very small in this range. Randy has an equation that will work exactly for specific gravity I think.