Ideal range is used when you DON'T have algae...it doesn't allow it to exist in the pool.
SLAM level FC is used when you HAVE algae. You have to have much higher levels to kill it.
Ideal range with algae, just slows the growth. Doesn't kill it.
Buy 15 gallons. You may use more you may use less. All depends on starting state. I used 43 gallons when I first came here. I have not slammed since.
You need to get the kit ordered.
If you don't have a SWG, get this. Link-->
TF-Pro
If you do have SWG, get this. Link-->
TF-Pro Salt
Order it now.
Add 5ppm of liquid chlorine per day until the kit arrives. Nothing else.