Preventive Care--When do you first notice algae?

[HouTex]

I was at a hotel yesterday on business and I passed by the hotel's swimming pool. The water was clear, but it was green as grass. No algae was floating on the surface and except for the green color the water looked clean. My question is how to you know when you are first starting to get algae? I would have thought that the first sign was cloudy water. But this water was clear--just green. Is the change to green color the first sign of algae? Does a green pool necessarily have algae? Was it something else?

 

[JasonLion]

Clear green water can be algae or metals in the water. Algae will make the water at least a little more dull than usual, so clear sparkling water is always metals. Even small amounts of algae can color the water green without it being obviously cloudy, but it will be a bit dull or lacking sparkle.

 

[HouTex]

Here is the picture of the pool (figured out how to reduce the file size).

 

[JasonLion]

That looks like metals, but it is difficult to be sure from the picture.

 

[mx702]

Looks inviting :lol:

 

[Flotsam]

NASTY!!!!

Where is this so I don't book a room there!!! (I'll understand if you don't actually call them out).