By default, pool will adjust the difficulty of your miner automatically over time until you have from 5 to 15 submits per minute. It's a good trade off between bandwidth and accuracy.
You can also set a fixed custom difficulty using the password parameter. For example, if you want to set the difficulty to 0.5, you would use:
-o stratum+tcp://stratum.granatgas-pool.info:3433 -u wallet_adress -p d=0.5
Here are the accepted values for the custom diff:
you can set diff range for X11 from 0.002 to what do yo want to set
Note: if you are a big miner 1ghs<10ghs please use fixed diff more than 1
If the difficulty is set higher than one of the a mined coins, it will be forced down to fit the lowest coin's difficulty.