Need help on hydrometer test

[Jameschen6]

I have never used the Sodium Carbonate before for the test. I have alwasys made the solution on the day I need. The pH of the disperse solution of the one I made today was 6.88. (48g/L). Why it is so low or it is suposed like this. I need Sodium Carbonate, right? I checked my supplier websites. This chemical seems to be not popular. Where I can find it and what is the grade I should buy?
Sodium Carbonate, anhydrous Light (Soda Ash)
Sodium Carbonate, anhydrous Dense (Soda Ash)
Sodium Carbonate, monohydrate

 

[Jameschen6]

I am in Toronto

 

[TigerGuy]

What hydrometer test are you running? For ASTM D422, you should use sodium hexametaphosphate. It's easily available from a chemical supply company.

 

[Jameschen6]

OK, Let simplise the question. The pH is 6.65 measured imediately after the making of the solution. Should I adjust the pH by mean of Sodium Carbonate?