The straps from our winter cover our leaving black marks on our stamped pad around our pool. We have our pool closed every season by the pool company that installed the pool. This will be our 3rd pool’s closing coming up. I wanted to reseal our concrete decking before we close this season but I need to get these marks out first. I have tried power washing these marks off with no luck. I also used mineral spirits and a wire brush but the marks/stains just seem to move out with the mineral spirits (pic below) 
Does anyone have this problem with their straps leaving marks on their decking? Any help in resolving my issue would be greatly appreciated!
