I don't know if there's any way to validate the precision of the bucket test, without expensive and elaborate lab equipped processes. If anyone has attempted such a thing, I haven't heard about it. (Of course, I have not read every post here, much less on TFP.)

But . . . it should be very close. There are two things you can do to improve the accuracy of your testing:
1. Cut the bucket off, so the lip of the bucket is only 2 - 3" above the pool water level. (Alternatively, you can arrange the bucket on stacked concrete blocks and pavers, to accomplish the same thing.)

2. Weight the bucket with a bit of stone or brick so you can set the water level in the bucket to the same as it is in the pool.
If you want to compare temperatures between pool water and bucket water . . . or just want an accurate pool temp reading, I can recommend these:
Habor Cooking Thermometer w/ 5.5" Probe
I have 3 - 4 of them that I've accumulated as part of my yogurt making gear, and they are cheap, accurate, and work well. One caution -- they are only water-resistant, not water-proof.
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But . . . after all that, I'm betting you have a actual leak. (Sorry!)

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