This is a very easy ...

This is a very easy situation.

I dont know why people are still promoting bleach, chlorine etc for drinking water disinfection. Your issue is Algae, here is my approach. 

Immedeately after your carbon fiteration install GoodlifeUV system. GoodlifeUV will ensure that there are no live bacteria/algae passing out of the UV outlet. GoodlifeUV is very different from the conventional UV systems and the there is "NO coating of quartz sleeves" that happens in GoodlifeUV systems.

As many have rightly suggested your storage tank water should be deprived of sunlight. Cover it up. In case there is long storage time in the  treated water tank then have another GoodlifeUV installed at your tank outlet for added safety.

No need to add any chemicals like Chlorine, no need for monitoring chemical dosage, etc.

GoodlifeUV is now available from the UAE.