How to make equal density pool dye without diffusion 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.
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.