Why has my pool water turned cloudy?

A few days a go, we took the pool cover off of our pool (15ft intex pool, it's an above ground pool but has been put into the ground and decking) and we found that it had gone green. We went to our nearest shop that sells swimming pool chemicals and we asked one both shoppers that was purchasing chemicals for the pool what we needed to get rid of the green and he told us we needed shock chlorine to get rid of the green stuff, so we bought a 4kg box of it and used it when we got home, now this worked and cleared all of the green from the pool, BUT now it has gone cloudy. Why? (: