Trying to spot the tear can be a dog depending on the liner pattern. As many times as I looked right at mine I didn't see it until I knew exactly where to look from the dye test. And this was with perfectly clear water. I scarfed my dye tablets from a GE chem lab years ago. I found ocean dye markers on-line and assumed a dive shop should have something but obviously not. I guess you would have to take them apart to get to the dye. Don't know how they are constructed. Food coloring is expensive. Something I've suggested over the years is raw beets. Chop them up and boil them and you have a concentrated red dye. Pretty cheap and you can make as much as you want...then eat the beets.
Al