It certainly sounds like a small leak. Plaster is put on wet and 12 days is a long time to blame the plaster. But I use to live in Northern Ca and have family and friends there and it was 100 degrees on the weekend. Was anybody swimming in it....pretty normal to loose an inch of water from kids swimming and jumping.

Was it leaking before it was replastered?

Before they replastered did they do a pre-plaster prep and reseal around all the pipes? Did you check your equipment pad and see any places where some older equipment that might have been sitting for awhile unrun might be leaking around seals onto the pad? Those are some obvious things. After that, the only way is to complain and tell them to send a diver over to check for leaks. I don't know about your plaster contract but mine said they aren't responsible for leaks.

Barco,

Thanks for the response. You reponse is much much quicker than my pool contractor. ;-)

To answer your question:

1. I don't think my pool was leaking before replastered. I used to fill the pool only once a week during the hot summer in nor cal.
2. I also had my plumbing redone prior to plastering, new light fixture too.
3. No one is swimming in it yet. But I did brush the pool twice a day and might have made the water level gone up to the drain hole.

More info:
My new pool light is tripping the GFIC easily.
More question:
Is the pool light niche (where the pool light is inserted) supposed to be filled with water inside?

Thanks again.

The vase may not have a large enough opening to give you an accurate read on evaporation. Try doing the same test with a large bucket. The longer the test the more accurate the read.

Is the light the only thing on the GFI? If not, unplug everything else and see if it still trips. If it does still trip get the PB back out there to fix the light or replace the GFI.

The niche does fill with water, that's normal.

Hmm, you had your plumbing completely redone? Was it pressure checked before the pool was plastered?