Stamped concrete bleached under where pool cover was

[towacodaddy]

I don't see a topic specific to pool decks, so I'm posting it here to see if anyone can help me out.

So when we took the cover off the pool last week, the stamped concrete underneath where the pool cover was is bleached (see photo). At first I thought the rest of the pool deck was just dirty, but I power washed it and that didn't help. Any ideas? Thanks in advance!

Andy

 

[cowboycasey]

while it does look bleached I think it is just the opposite, the sun has darkened the rest of the deck and did not get under the cover..

 

[Richard320]

I suspect Cowboy Casey may be right. Mix up a little Muriatic Acid about 1:8 and find a spot on the patio that isn't too noticeable and sprinkle some on, It'll fizz. Hose it off right away. After it's dry, see if it matches the pool border. If yes, your weekend will be spent with a deck brush and a spray bottle of acid.

 

[alben]

The concrete under my safety cover is much lighter. Inspecting the concrete closely, the concrete under the cover is clean and has no dark algae. The exposed concrete in the yard and driveway has a small amount of black algae on it, hence making it slightly darker. Also noticed the concrete is lighter under the spots where we park our cars. I've cleaned the concrete by hosing it down with water, pouring some bleach on it, and scrubbing lightly with a nylon bristle push broom. Be careful to not get any on your plantings.

 

[towacodaddy]

Thanks a lot for your replies, guys. I'll give that a try & let you know how it goes!