The theory is sodium levels when using 2 part dosing can result in an excess of sodium chloride and not enough of the other elements in the water over time that water changes will not necessarily correct. Dosing a ABC 2 part, kalk, or using a CaRx will. Additionally, sodium chloride should be about 70% of your total salinity.
At least this is my basic understanding and reasoning for measuring Sodium.
Sodium Chloride would account for around 70% of the salinity in perfectly balanced SW.
So the math to convert the Sodium reading to Salinity would be pretty straight forward but since many aquariums are not balanced you would get a discrepancy. If you compared the calculated reading versus an accurate salinity checker like the Hanna or Aquatronica. That difference would give you an idea of how far off your Ionic balance is and getting the numbers to match would be an indicator that your tank is in balance with Sodium Chloride making up approx 70% of the salinity reading in your water.
The question is will GHL include in the software an automatic calculation system. Secondly I have no idea how good the GHL salinity probe is, but if it very precise it would be a great tool when used in combination with the Sodium reading. It would give GHL owners unique insight into how balanced their two part system is and it would be automatic. The rest of us would just have to compare readings until we get them to match.
Can someone tell me how to calculate this balance?
I have a sodium balance of 10600mg/l, seems in the green area if I need to believe my ION Director but I would like to calculate it myself.
Someone who knows how to calculate this balance depending on overall salinity?
You have the backwards calculation here - maybe it will help you. Another interesting thing is that ION director give you the 4 most important ions for salinity calculations between the index finger and the thumb. Using the tool in the link - you can get a picture if you are near or far behind the salinity you want. Note also the row with the normalised value