2% is a good place to start.. Each pool is different.. You just need to test and see where you are... After you use the spa, check the FC level of the spa water. If low, then raise your spa % a little.. If too much FC, then decrease the %... I personally would rather run a little "hot" on the spa FC rather then having the FC be too low.
I second this. Use pool math to determine the %. You’ll need a good estimate of the gallons of the pool vs spa. I’m assuming the 13k gallons is for both? I change my % settings based on my PPM loss per day, which changes.
Spa is attached to the pool. There is a spill over. there is a jet on the spa floor that goes above and acts as a fountain.
So the spa jet works concurrently with the rest of the pool jets. all connected
The purpose of the Spa % is to prevent you from soaking in very high FC when in the Spa mode... This is why you need to check it right after you get out of the spa.. If really high you should turn the % down.. If about the same as the pool water leave it alone.. If very low, crank it up a little...