What Makes the Algae Grow?
Algae grows from the algae spores. The spores can come into the pool through contaminated swimsuits or even wind and rain. This is unpreventable, but it can be taken care of easily.
When the spores come into the pool, they will usually get cleaned up by the filter. However, stagnant water will let the spores sit in the water. As well, low chlorine and un-adjusted pH levels can help the algae grow.