You can find my FRAM library here - GitHub - RobTillaart/FRAM_I2C: Arduino library for I2C FRAM
If you have a range of 150 - 175 °F there are two options:
either you use 150.0 ..175.5 => 255 values in one byte with decimal precision
uint8_t codedValue = (TF - 150.0) * 10;
float TF = (codedValue * 0.1) + 150:
or
you use the range 0 - 255°F just as integer.
The latter has the advantage that you see when the tank is cooling down or overheating.
So it allows you to add safety margins.
You can also select something in between like the range from 120-200 °F with one decimal
(steps of 0.2°F) that balances precision and detection of over/underheating.