prevent the algae from forming wasn t calibrated correctly. we had to figure out exactly how much ozone to inject into the water to kill the nutrients that the algae feeds on and because we had it to low at the beginning, algae took hold. i used to clean pools as an engineer and i know what can happen with this. one little change and the algae is everywhere. reporter: it will take a few days for clean-up to be completed and then three more days for the pool to be refilled. all the work costs about $100,000, the money coming out of national park service s maintenance budget. we have to do this once a year. reporter: the renovation project included reinforcing the bottom of the pool to prevent millions of gallons from leaking out every month. it also included new l.e.d. lights and handicapped accessible walkways, but the green project turning green wasn t in the plan. many tourists say they understand. i think it s money well spent. unfortunately we have these misha