Adding Mag

[Piazzon12]

Does adding mag sulphate or hexahydrate affect salinity at all? I just added 3 cups and later noticed my salinity was a little high... however the events may have been unrelated, and it may have just already been a little high.
And yes Im using a crappy hydrometer, so theres no need to go into that debate

 

[Kent E]

Yes. You are adding magnesium and chloride.

I just dump out some water every once in a while. Of course frequent water changes too.

 

[drbronx]

To be most clear in our understanding, we should probably refer to specific gravity rather than salinity. Specific gravity is the ratio of density of ions in fresh water. These ions are different salts, minerals and elements. So therefore, any time we add elements such as Mg, Ca, etc., it will influence ionic density, but typically will balance out over time as they get incorporated into the system.

 

[daveverdo]

Actually, specific gravity has nothing to do with ions. Specific gravity is the ratio of the density of a material to the density of pure water when both materials are at the same temperature. It essentially is a measure of density with no units. You can give the specific gravity of a rock or chunk of wood, neither has any ions.

Now in the specific case of saltwater, drbronx is correct that higher ion content generally coincides with higher specific gravity, but not always. Ammonia (NH3) when dissolved in water results in a specific gravity lower than 1.0.

In the case of your question, it all depends on how you are adding the materials. If you dissolve them in fresh water and then add that to the tank it should not change the SG significantly. If you add it directly to the tank or mix it with saltwater it will raise the SG.

Dave

 

[drbronx]

Thanks for the excellent clarification. I defer to the physics professor