I have a leak I have been struggling to find in my in-ground pool. I am losing about 1/4" of water per day and I believe the issue is one of the fittings in the bottom of the pool. There are two main drain fittings and one deep pot that has two pipe plugs that if removed allows groundwater to enter into the pool to prevent the forces of buoyancy from floating the shell out of the ground like a boat when the pool is drained.

I want to make a dye that is has a specific gravity equal to water that has minimal to no diffusion. It has to be safe because it will be introduced to the pool water.

The only thing I have found that is almost the same gravity of freshwater is beer, or milk. The problem with those is the diffusion rate. I was hoping to find something that I could mix with dye that had a specific gravity (I hope that is right) as near to freshwater as possible that wouldn't diffuse when introduced to freshwater.

My intention, hope, is that I would place a blob of dye over these plugged fittings and if there was a leak around the fitting it would eventually suck that dye into it. It could take 15 minutes or more for the dye to be pulled into the leak, so it has to have a very slow diffusion rate.

  • $\begingroup$ 1/4 '' is not much, could it be due to evaporation? $\endgroup$
    – porphyrin
    Commented Jan 15, 2019 at 9:38
  • $\begingroup$ I have performed a bucket test as well, and the water level decreases at a higher rate than the water in the bucket does. I filled the pool to a known level (a pencil mark) this morning at 6am. At 5pm, eleven hours later, the level in the pool has decreased by a quarter-inch. I have also set a clear pitcher on one of the pool steps and filled it with water to match the water level of the pool to conduct another bucket test. $\endgroup$ Commented Jan 15, 2019 at 23:04
  • $\begingroup$ Another idea would to introduce something that has a slightly higher specific gravity (or density) of freshwater that would diffuse widely and cover the entire bottom of the pool. My theory in this would be the dye would then be pulled into the leak and there would be a clear hole in the dye to indicate the approximate position of the leak. $\endgroup$ Commented Jan 15, 2019 at 23:09
  • $\begingroup$ In my kitchen I filled a clear glass bowl with tap water. I then mixed red and blue dye into a small bowl of lactulose free whole milk to make a purple mixture. I used a hypodermic needle to slowly introduce the mixture near the bottom of the bowl to observe the diffusion rate. The mixture slowly diffused across the entire bottom of the bowl, but settled, leaving a thin purple sediment like layer across the bottom of the bowl. So, the specific gravity/density of this mixture is slightly greater than water (desired), but the diffusion rate is too high (undesired). $\endgroup$ Commented Jan 15, 2019 at 23:39
  • $\begingroup$ If the DIY aspect is not crucial why not to go for a pool dye? It can be some fun especially if children are around. Lot of us here have ideas of what they are but to avoid any safety concern I would go for dyes sold as pool dyes. Saw they aren't expensive. $\endgroup$
    – Alchimista
    Commented Jan 18, 2019 at 10:04

1 Answer 1


Whole milk with food coloring solved my problem. Whole milk has a specific gravity of 1.01, which allowed it to settle to the bottom around the main drains. The diffusion rate was extremely slow over regular pool dye, which allowed the dyed milk to linger around the drains for an extended period of time (5+ minutes) to allow for the detection of the slow leak.


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