Most of the time when people talk about optical density they are talking about laboratory results using a spectrophotometer and glass cuvettes, and measuring the light passing through a one-centimeter lightpath. But it certainly also applies in the real world to larger systems. A month ago at this pool I could put in a swimming pool net with a yellow rim and watch it disappear within the first four inches. It was green!
But, just a reminder, if the water is not toxic to the point where algae will grow, it is likely to be far less toxic to us. Today I went “prepared” because the client had sent me a surprised email that it was clearing up! The net in the first picture is about 8 feet down.
The next picture is 4 feet down in the shallow end. You can clearly see the bottom.
The last picture is showing that the pool still looks somewhat green but it is definitely clearing up.
Every two fold difference that I can see through the water is equal to 50% of the current biomass being removed. So when the pool went from 4 to 8 inches that was the first 50% of the algae biomass removed. 16 inches another 50% of the 50% that is still remaining (or three-quarters of the original amount – 75% total) of the biomass removed. 32 inches=50%+25%+12.5% (87.5%) 64inches=94% removed in two weeks! With absolutely no toxins.
Bob