As my name suggests - I am new to pool ownership. I have a 16 X 32 in ground pool. Based on the information that I have already read on the forum (thank you!) - I've finally gotten the chemistry right. My question: there still remains some black spots on the bottom/sides of my pool. I've take a brush to remove them, but some seem very persistent in wanting to stay. Is there an easier solution rather than taxing my lungs swimming to the bottom and brushing them away? Thank you!