Found the
ReefKeeping and DIY 35 ppm standard solution procedure. Thanks all.
"This 3.65 weight percent sodium chloride solution can be made by dissolving 3.65 grams of sodium chloride in 96.35 grams (mL) of purified freshwater. This recipe can be scaled to any appropriate size if suitable instruments are available (36.5 grams in 963.5 grams (mL) of water, 0.365 grams in 9.635 g (mL) of water, etc.).
This concentration roughly corresponds to ¼ cup (73.1 g) of Morton's Iodized Salt dissolved into two liters (2000 g) of water (giving very slightly more than 2 L of total volume).
For a rougher measurement in the absence of an accurate water volume or weight measurement:
1. Measure ¼ cup of Morton's Iodized Salt (about 73.1 g).
2. Add one teaspoon of salt (making about 79.3 g total salt).
3. Measure the full volume of a plastic 2 L Coke or Diet Coke bottle filled with purified freshwater (about 2104.4 g).
4. Dissolve the total salt (79.3 g) in the total water volume (2104 g) to make an approximately 3.65 weight percent solution of NaCl. The volume of this solution will be slightly larger than the Coke bottle, so dissolve it in another container.
[Note: the standard described here using soft drink bottles is subject to variation in the volume of the bottle. It turns out that such bottles can vary in total volume, and this can lead to at least a one ppt error in the salinity of standards matched to seawater of 35 ppt salinity. Standards made with accurate measurements of salt and water, however, will accurately match 35 ppt.]
"
