format number to go 6 decimal places on the right

I am currently using: =Sum(ToNumber([Tons Emitted])) + FormatNumber([Tons Emitted];"######.######")

I also tried =Sum([Tons Emitted]) + FormatNumber([Tons Emitted];"######.######")

I am getting the results to where half of my numbers are right, the other half it repeats the number as: 12345.612345.6

and I get values with two decimal places like:0.62.617708

What can I do to take a sum of numbers and have them show the number going out at a minimum of 6 decimals to the right??

Thank you

Angela