specific gravity table

[douggiestyle]

ive noticed that my specific gravity can drop from 1.025 to 1.024 with as little as minus 1.5 gallon of water in an eighty gallon tank. is this real or is this an example of bad testing? or am i fretting over nothing? hence my topic, is there a table listing changes in specific gravity with losses or additions?

 

[scuba_steve]

sounds right to me !! not to worry imo

 

[fishfreek]

How are you testing your SG? Refractometer or Hydrometer?

Are you saying your tanks SG goes down when you have evaporation?

 

[douggiestyle]

Are you saying your tanks SG goes down when you have evaporation?

sorry, reverse that

 

[fishfreek]

Oh ok. Thats what I figured.

How are you testing your water? For example swing arm hydomoters have some degree of error and two tests could turn up a different SG reading thats off by .01 or even .02

 

[douggiestyle]

How are you testing your water? For example swing arm hydomoters

yes a deep six hydrometer. my results are consistant.

i guess my question is if there is a table that explains additions and how they affect sg.for instance, say you have one gallon of water with a teperature of a and sg is b adding c amount of fresh water will lower sg to d. or at least something to that effect

 

[William]

Salt only leaves your tank if you do a water change, salt stays in the water through evaporation.. which is why you top off almost every day with freshwater.


So if you take out to much water due to evaporation, Your Salt level will go up.


If you add more than your regular ammount of fresh water to the tank, then your salt will decrease.

 

[douggiestyle]

So if you take out to much water due to evaporation, Your Salt level will go up.


If you add more than your regular ammount of fresh water to the tank, then your salt will decrease

ah yes
but maybe someone has a table or an equation explaining this in mathematical terms? it would make creating water for water changes easier instead of guessing. also it would make udjusting salinity in the tank more predictable.
this would also allow one calculate the concentration of your salt mix as well as other things.

its the chemist in me.

 

[cmor1701d]

it would make creating water for water changes easier instead of guessing.

There shouldn't be any guessing. If you keep SG at 1.025 and make up for evaporation with RO water, then your SG will remain at 1.025.

For water changes, make the mix at SG of 1.025.

I change out 12-15 gallons in my 125. I don't need to precisely measure the volume of water because whether it's 12 gallons or 15 or somewhere in between I just mix it to 1.025SG and then do a water change.

Different salt mixes require different amounts to achieve the same SG. Follow the directions and adjust as needed.

 

[douggiestyle]

For water changes, make the mix at SG of 1.025

so when you mix your water for a water change the sg is right on the first time? if its off do you guess how much more salt or fresh water to add.

so far ive gleemed that sg is the density(mass divided by volume) divided by the density of pure water at 60F (1.000). seeing that we are dealing with the specific gravity of water then you simply use its density only (mass divided by volume). adjustments are needed as temperature rises, the water expands there for becoming less dense.
therefore if you add 25g of salt mix to 1000cc of water at 60F the water weighs 1025g. 1025g/1000cc (m/v) the final product is sg of 1.025.

i will work this out myself and add it to this post later.

 

[cmor1701d]

if its off do you guess how much more salt or fresh water to add

YES!

therefore if you add 25g of salt mix to 1000cc of water at 60F the water weighs 1025g. 1025g/1000cc (m/v) the final product is sg of 1.025.

Not necessarily true.
Specific gravitycompares the density of a mineral to the density of water. If a mineral has a SG of 2, then it is twice as dense as water. If a mineral has a SG of 3 then it is three times as dense as water. A salt MIX is made of salt and many other minerals, therefore the same quantity of different mixes could yield a different SG at the same temperature.

I start with the directions on the package, mix till disolved, wait a couple of hours, test with a refractometer, then adjust if needed.

 

[cmor1701d]

The specific gravity of a substance is a comparison of its density to that of water A marine salt mix contains not only salt but many minerals, each with their own SG.

Specific gravity compares the density of a mineral to the density of water. If a mineral has a SG of 2, then it is twice as dense as water. If a mineral has a SG of 3 then it is three times as dense as water.

Because the various commercial sw mixes contain differing amounts of the numerous trace minerals, a given quantity of mix from different manufacturers or even different batches from the same manufacturer will produce a slightly different SG.

Testing a mix with a refractometer is the only way to be truly accurate.

 

[douggiestyle]

Specific gravitycompares the density of a mineral to the density of water.

i said the exact same thing.

sg is the density(mass divided by volume) divided by the density of pure water at 60F (1.000).

Not necessarily true.

100% true except for one factor. that i chose to leave out, for simplicities sake, adding the volume of the salt mix to the volume of the water. i would suspect that different salt mixes may have radically different concentrations when using a measuring cup (the amount of air, grain size, water content). but i believe that when measuring the "true density" of different salt mixes one would find that they very similar.

im not trying to start an argument, but i do like a good debate. that is how good questions are created

my whole point of this post was to stop guessing and be more scientific about my approach. i used to work in a lab for sony mixing chemicals and such (not much schooling in this subject, just worked my way up the ladder) and everything was a known, to some extent. i was able to fill a 500l tank with di water in two hours. this was in a chart. you set your watch or else get a mop. if you couldnt find a chart or table you made your own. to achieve a specific concentration you read the specs, you measured and mixed.

 

[William]

whoa, this is getting way to technical for my simple mind! :?

 

[douggiestyle]

ause the various commercial sw mixes contain differing amounts of the numerous trace minerals, a given quantity of mix from different manufacturers or even different batches from the same manufacturer will produce a slightly different SG.

i agree but trace usually means barely identifiable. this could mean that a pinch of something could be added to a five gallon bucket. having an effect that probably even the most accurate means of testing density would would show know change.

im still working on my table.

 

[douggiestyle]

whoa, this is getting way to technical for my simple mind!

sorry i just wantedknow how much pure water needs to be added to five gallons of salt water to change the sg from 1.027 to 1.025. with out guessing. thought maybe someone had figuered this out already

 

[cmor1701d]

im still working on my table.

Please post it when complete. Don't forget to take temperature into account too.

 

[douggiestyle]

will do

 

[douggiestyle]

Sorry its been so long.
Ive had no success in coming up with a formula. after a good bit of research, boning up on my chemistry, and a lot of pencil lead and eraser leavings. ive come up with nothing. i gave up. ther was definately something that i repeeatedly left out?
no matter, it beat twideling my thumbs.

i did buy a scale at a cooking store and it turned my guesses into very accurate assumptions. for instance, when mixing change water i add 1620g of IO to a ten gallon tank of water and its right on the money every time. every thing i add to my tank other than food i now weigh and record in a log book. it may seem rather anal retentive but now when something goes a bit awry i can honestly know that its not something that i added in excess. i would recomend a scale.

sorry i never came up with an accurate table.

may i have some tabasco sauce with my hat!!!

 

[douggiestyle]

Sorry its been so long.
Ive had no success in coming up with a formula. after a good bit of research, boning up on my chemistry, and a lot of pencil lead and eraser leavings. ive come up with nothing. i gave up. ther was definately something that i repeeatedly left out?
no matter, it beat twideling my thumbs.

i did buy a scale at a cooking store and it turned my guesses into very accurate assumptions. for instance, when mixing change water i add 1620g of IO to a ten gallon tank of water and its right on the money every time. every thing i add to my tank other than food i now weigh and record in a log book. it may seem rather anal retentive but now when something goes a bit awry i can honestly know that its not something that i added in excess. i would recomend a scale.

sorry i never came up with an accurate table.

may i have some tabasco sauce with my hat!!!