Manually adjusting for temperature

[someone]

I have a TDS meter for measuring nutrient solution, but I know fro research and experimentation that the measurement is dependent on the temperature of the solution, so when the temperature goes up, the reading goes up for the same actual amount of nutrient. How would I, for example, find the actual concentration nutrient if my meter reads 800 PPM NaCL and the temperature is 85 F? I have seen TDS meters that have built in thermometers, and they can do this automatically, so I know its theoretically possible.