The decking around our pool is salt finished concrete. After a recent rain, some of the oak pollen sat on the concrete for maybe a few hours until we washed it off in the morning. There's one patch of the concrete that stained and power washing won't clean it. It's strange bc it's just this one section of the concrete, which also happens to be the second batch of concrete they had to bring in at the last second because they ran out of the first. I'm wondering if this means there's something wrong with the second concrete mixture. Does this indicate there's something wrong with the concrete or should we just except this "as is"? (You can see in the picture, the pool contractor has had to remove the coping and will reinstall bc the stone was sealed per the manufacturer's specifications.)