to me they look like tiny grains of white rice
If it doesn't have the triangle head it's not planaria. Please go here and read post #12.
The reason you need to be SURE what it is is because #1 most other flat worms that are similar are harmless and #2 the meds that kill planaria won't kill some of these other worms.
Also lots of flat white worms in the aquarium are going to look like grains of rice, that's not really descriptive enough to help determine what you have.