Swimming pool leak - that's not really a leak

Here is a quick example of a problem that was (apparently) overlooked for quite a long time by several swimming pool professionals trying to figure out why this pool was losing water.

This is the pool side termination of an 'overflow' pipe from a spa which was installed higher than, and separated from, the pool. The system is built with the pool and spa sharing the same equipment. Under normal, everyday operating conditions a small amount of water is diverted from the pool through a 'bypass' pipe at the equipment and into the spa, to keep the spa water 'fresh' and chlorinated, causing them to be 'the same body of water'.
This overflow pipe is installed exactly at the high point in the spa where we want to maintain the water level. It is common for this pipe to be open ended at the spa (recessed in the wall out of site) and also open ended at the pool (with only a grate covering it). The bypass water flows back into the pool (only by gravity) through this overflow pipe, taking any floating debris with it. When this debris gets to the grate at the pool it gathers, gradually blocking the water flow. Then the water overfills the spa and pours out onto the ground, or wherever it wants to go - away from the pool, causing the pool to 'lose water'.

The purpose of this post is to illustrate the importance of investigating deeper than just what we see from standing on the deck above the pool. The 'bypass/overflow' concept will be discussed more thoroughly in a later post.

I will try to be gentile on my professional colleagues because, just by looking at this grate form the deck it seems very open with just a few pieces of debris showing through. I was also tempted to look elsewhere for a problem at first. But, since I am slightly obsessive compulsive, I had to confirm that this grate was completely clear before I moved on to investigate something else, so I took it off. It's quick and easy to do, you can see there are just two screws holding it in place.
I have to think that this grate looks like it is mostly clear because the technician has been brushing over it, removing the debris that can be seen, then declaring it to be "clean" - easily understood.

This pool had nothing floating in it prior to me removing the grate, nor did the deck have anything on it before this picture. All of what you see on and around the grate came from behind it. The gravity flow of water from the spa into the pool was definitely completely blocked. So, the water from the bypass was not getting into the pool, it was flowing over the shortest wall into the cover box and out the drain pipe, which is out of site. Causing even the professionals to think there was a leak in the system somewhere underground.

This is just a pipe coming from the spa, the reasons for having a grate in the pool are so; it isn't ugly, and it isn't a potential hazard - keeping a small child's limb from getting caught inside. Because this pipe is open ended at the spa, without a grate, it allows debris to enter and flow to this point.
This leak problem seems to have been solved just by keeping the grate clean from behind.
My opinion: Install some type of grate at the spa so that the debris can be easily seen and cleaned from the deck.
Thank you for reading!