Builder says originally how there are no 90 deg in his pool. Then when plumbed I brought some in the steel to his attention and he said oh no the returns can have 90's just not feeds. He said to prevent a 90 he uses a swoop 45. Ok I buy that but today after a lot of plumbing is put in I went out and find several feed lines with 90's. Of course they had buried the joints but i uncovered them when I got curious. So when is it ok to use 90's?