My guess is a pair of eyes close to the problem will spot it. Once you see something suspicious then dye may work to confirm. Turbulence is what you'll be fighting with dye when someone is in the water. The three slits that were at my deep end were not obvious from the surface until I knew where they were. Otherwise they blended into the liner pattern. If my face was 6" away they would have been seen but 8 feet...forget it. You have nothing to lose...go for it and
Good Luck.
Al