Is there a chart for specific gravity as a function of salt volume per water volume

[Corn-Picker]

I have 20 gal of saltwater in my tank. The specific gravity is 1.020. I want an SG of ~1.022. Is there a chart somewhere that has SG as a function of salt added? I googled but couldn't find anything.

To get the SG of 1.020 I simply added 1/2 cup of salt for every gallon of deionized water added. As soon as I get my SG in the sweet spot I'm going to add ~5" of Tropical Play Sand to the tank. Then, after the sand settles, I'll start the cycle with rotting cocktail shrimp.

To answer the obvious question, the reason I'm not adding salt then testing the water after a few minutes, is because I don't have a hydrometer. I can't justify paying $20 for such a cheap piece of plastic. So, I measure my SG by filling up a 100 ml graduated cylinder and using a high prescision balance I have access to where I work. Therefore, it takes me about a day to know if my SG is right and to adjust accordingly.

 

[OrionGirl]

The volume/weight of salt varies with humidity. So, there is not a standard volume/mass needed to get a specific concentration of dissolved salt in water. You can get close, but really, a hydrometer or refractometer is required equipment for brackish and marine tanks.

 

[Corn-Picker]

I added one cup of salt to my 20 gallons of salt water last night and the SG turned out to be 1.023, which is exactly where I was aiming for.

OnionGirl, I appreciate the concern about buying a hydrometer or refractometer, but my 100 ml graduated cylinder and electronic balance that measures to ten-thousandths of a gram is amazingly accurate. 100 ml of water weighed in at 102.30xx grams today, exactly an SG of 1.023

 

[OrionGirl]

Using the scale to determine salinity is fine--just don't count on it always being one cup. I was thinking you wanted a specific volume or weight to use in mixing, rather than using the scale in the same fashion as a hydrometer.

 

[mogurnda]

The thing is that a cheap plastic hydrometer takes less than a minute to check your specific gravity. If you calibrate it with a refractometer or your balance, then it will be accurate enough. When you're compensating for evaporation, the balance system may be too slow to be workable.