Rock pool weighs drown us

we had a rock pool built by Rockscape in Cape Town. Renier the owner is a very nce guy and very onliging and helpful, the pool at the end of the day did not turn out as expected but we accepted it as such as he made up for the fou - par by adding in some additional \rock features". All looked great until a few months later the pool which was regularly checked turned green and took ages to be cleared"