I also have a glitch downstairs by the pools...I cant get rid of it and dont know whats causing it!
Sorry to respond late but I wanted to help because the same glitch happened to me and after a few trillion trials I figured out how to fix it. Delete the 2 rounded edges of the pool where the green glitch is. Also delete the floor tiles around the mysterious blue hole that is left. Use the square pool builder tool to cover the entire mysterious blue hole with a 3 x 1 tiny square pool (in your case), then delete it using the ctrl-click function rather than undo. After you delete the tiny pool you just built, the land should be back to normal and then you can go back and redo the two rounded edges and the floor tiles with out the green glitch. I DLed your house from the exchange so I could make sure I did it right and yep, it did work. Great house, btw. I'm gonna keep it for my legacy fam when they get disgustingly rich.
For some reason, the rounded edge pool building tool doesn't like for you to place it on/near floor tiles. You've got to put the rounded pool edges down first and then the floor.
edited for typo.