Creating either/or like statement when user inputs in specific numerica control

Hi guys,

I'm not 100% sure how to word it but I want to control the numeric inputs as so when user is inputting a value into a specific box, the rest would be grey out and be disabled.

Say the user input a value onto the "Desired Flow Total," the rest of the input would be grey out and disabled, allowing just a single value input... not sure if I'm wording this correctly or not.