This is a stand alone gunite spa. All the plumbing tested ok. I dye tested and found nothing. I know in a 24hr period it lost 1/4 inch which is only 8 gallons of water. I have also tried the hydrophone with no luck.

1. Clean the edge of every pipe fitting, light, drain sump, bond between skimmer and shell, tiles and anything else that penetrates the shell with a toothbrush. Hopefully this will make the leak larger and possible to detect with dye testing.
2. Or try plan B: Fix-A-Leak sealant, circulate it throughout the spa (follow directions and by-pass the filter) It will find and seal the leak, afterwards you could reinspect, the cured sealant will look white, like a white line along the edge of a fitting.
The smaller the leak, the harder to find.
Bruce
PoolRepairDiver.com

I'm with Bruce, a leak that small is gonna be almost impossible to find. 8 gallons a day translates to .33 gal per hour - very minimal, we won't even attempt to find one this small. Locating this leak with pressure testing or dye is unlikely. You didn't mention, was the spa heated when you took your measurement?, that could affect your results.
If you want to do something, I'd recommend the shotgun approach - drain the spa and epoxy around all the skimmer throat, all the fittings and anything else that looks suspicious as well as putting butyl tape in the light conduit.

What is the water temperature?? Even in a cooler climate a quarter inch loss is probably evaporation.
If the water is 104 F and uncovered I would expect to see even more of a loss.

Had heated spas on commercial properties lose up to an inch a day. When I first started one job with 300 or so units was losing 3'' a day. Drove me crazy looking for a leak. Finally put a chain/lock on the courtyard, drained the spa into a pool that was not heated via a sump pump bringing temp down and set up an evap test. No leak

you need to inject air to open the small leak well, but make sure to get all the water out of the line try adding 20 psi of air pressure