Answer:

Has the pool store checked the nitrate and phosphate levels? Both or either of these could be contributing to the green pool water even in good conditions. It is not uncommon for heavy storms to have both in the water. It could also be due to "run-off" from the heavy storm - fertilizer or something similar washed into the pool by heavy rain. These are treated in different ways - phosphate with chemical remover and nitrates likely with a partial drain and refill depending on the level. As far as the question of weather it is safe to swim or not - make sure there is no particulate or suspended material in the water. Also make sure your filter and pump are operating omptimally and there are no stagnant areas of water. If everything is working well and levels test ok, it is likely safe to swim. Be aware of any irritation and leave promptly if you start to experience itchy eyes or skin, etc.