I have a long clear plastic tube that I use for this exact purpose. Hammer in a long stick in one spot and cable tie the tube to it. Measure exactly 3 feet up from the ground and put a mark on the tube with a sharpie, this is your reference point to which all other points will be leveled to. Cable tie the other end of the hose to a similar stick and mark the tube exactly 3 feet up from the bottom of the stick. FIll the tube with water.
Now when you walk around the perimeter, or anywhere in between, the bottom of the second stick will be level to the ground of the first when the water level on both tubes is exactly the same. You will need two people for the operation.
Leveling paver to paver with a bubble could cause you to be a bit off at the very end. Measuring across the entire pool with a water level will prevent this.
The easiest way is to mark all the posts and then dig out and put pavers in these spots, level to all the others. Then fill in between all the pavers with sand.
Remember, if you dig too much and need to backfill, do not do it with dirt, either use crushed rock or sand, the dirt will not compact well and settle over time.