Welcome to TFP!!!
You are doing great!
CYA 40 is perfect. If you want to use a bit less, you could increase your CYA to 50, but 40 is absolutely fine. For CYA of 40, keep your FC at 5-7ppm. NEVER let it get below (or near) 3, and you will avoid algae!
Read this and follow the chlorine/cya chart. Link-->
FC/CYA Levels
Two more recommendations
1) If you have a smartphone, download poolmath...will help you with chemical recommendation and additions. Link-->
PoolMath
2) Ditch the strips and get a good test kit. Having accurate readings on your pool water avoid a TON of issues that we see here. Link-->
Test Kits Compared
Enjoy the pool!