It sounds to me like you don't have enough chlorine for your CYA level. If you are using pucks (tabs), you are adding more CYA, and need even higher chlorine to compensate.
You don't need algaecide- you need more chlorine; how much depends on actual amount of CYA;
If you can get a water sample to a pool store, they can check your CYA level- then you'll know how much chlorine you need to maintain to shock (kill all the algae- probably for a few days, not just one dose!)
and then what level to keep to avoid algae in future...