How are you testing your water?
If you have a recommended kit (Link-->
Test Kits Compared)
Do #8 here and post the result:
Cyanuric acid (CYA) is the chemical name for the product commonly called “pool water stabilizer” … Read more…
www.troublefreepool.com
You need to maintain your FC according to your CYA. Link-->
FC/CYA Levels