Leak 1/2"/day per bucket test, 10k in-ground, pool light "good".

I read the article about leaks here first: Leak Detection - Trouble Free Pool (I didn't see the pool light conduit mentioned, which is technically not the pool shell or the plumbing, but should be emphasized, so please add this.)
I'm assuming that no air leak would cause 1/2" / day water loss. So I'm on the next step, to ensure it isn't in the plumbing, or if so, where. It leaks at a constant rate when pump is running 24x7, or off for 4 days. Can't see any leaks using food coloring dye around the skimmer. (I will be allowing the water to fall below the skimmer inlet to ensure I didn't miss it.)

  • How can I most easily "plug" the lines? I'm sure there are many ways, but looking for easy and cheap since I have 3 pressurized 2" and two 1/2" fountain outlets, and then 3 more 2" returns; skimmer, main drain, and side accessory.
  • Using dye when pool is perfectly still, has anyone ever detected a leak directly into one of the main inlets with dye?
  • When valves are severely restricting outflow, it seems this should be a good test to detect if the pipes were leaking, and you'd lose a lot more water. I could also increase the pump speed to increase the pressure, which should increase the leak rate as well. Shouldn't the increased return pressure show that if it leaked much faster, the leak was in the plumbing??
  • Is there a way to thicken the dye a bit so it won't disburse as quickly? I'm thinking of mixing dye with cooked corn starch so it would take over 10 seconds to disburse. I'd think that a hypodermic would be a better tool than a squeeze bottle. How thick? I will let you know if I try this.
I've had leaks at the pool light conduit before, and I'm fairly sure I've got no further leaks. Finding a suitable material for plugging around the wire in conduit is not easy. I've used fishing worm rubber before--Don't, or you will have a mess, as the chlorine turns the worms into a thick messy jelly that is very sticky. About four years ago I used pure silicon rubber, and that worked fairly well and cured underwater. The silicon would tear more easily after four years, but held up well enough to keep anything plugged. I used a caulking gun underwater and this seemed to work well. Note that it will not stick to the metal underwater, and it can be a mess to apply. I used saran wrap to form it around what I needed, and left the saran wrap in place for a week or more, which could then be removed, since the silicon had partially set by then.

Sealing materials for underwater pool leak research: Since I've had failures of different materials, and I didn't want to epoxy the conduit with the pool light wire. In my quest to find something that could be applied underwater that would stick, was not visually objectionable, remain flexible, and stand up to years of chlorine treatment, I came up empty. So, I wrote to several manufacturers, who listened intently to me detailed specs, (available on request), and forwarded it to the marketing departments. 3M surprisingly came back and flatly said that nothing they had, fit this criteria. But, they didn't see much of a market for such a material. Using silicon caulk works somewhat, But I can't see it being used where the skimmer or other material meets the pool surface. What is the best aftermarket material?
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