I have cement base under my lawn therefore my lawn has just 7 inches of soil and then below that it is fully covered with cement. This is done to prevent water seepage in my basement so I can't drill holes in it to improve drainage because then my basement may suffer from water seepage. As there is cement base during heavy rains due to poor drainage I can see green algae at some places in patches. After few days when sun falls on it it turns to black and looks very ugly. I just pour handful of soil over it to cover it up. So, basically I am just hiding the problem instead of solving it.
Is there any solution to algae? May be pouring diluted vinegar but I read it can harm the grass as well. I need some solution that can kill the algae but not my lawn.
Any help is appreciated.
So here is the picture I found from the internet. You can see the green colored substance in the picture. If I rub my fingers it feels Jelly like. This is exactly how it looks and once rain stops and sun falls on it it becomes completely black: