The walls and bottom are getting slick what should we do to solve the problem?

This is an indication that your unit is not producing enough free chlorine...
Big pools require up to 12 pump hrs with 10 chlorinating hrs. (depending on outside temperatures) and electrolytic cell must be maintained clean. If your unit is clean and you have the correct salt level, try this;
Brush your pool with pool pump and get all that slick stuff off.
Clean you filter...
Set your pump to run 12 hrs with 10 hrs of chlorinator. You will see results in 2 to 3 days..
Clean your filter again..
After pool water clears and chlorine level raises, adjust time as needed..

Hope this will do it for you. If it helped, please rate!!