Pool Leak - how to identify and fix

Ok.so here is my story...I opened my pool about a month ago
when we had a few days of 70+ degree weather. The water level
was a bit low but I didn't actually fill it until maybe two weeks ago
when I put in about 4 inches to a 500 SF pool surface. Last week
I thought it strange that the water level again seemed low so
I ran the hose in for 12 hours and filled it to the proper levels.

This week, I was amazed to see the water level back down to
below the skimmer holes. I think there must be a leak somewhere
but how do you go about identifying where and does anyone
have an idea on how much it potentially might cost to fix?

Any suggestions or comments by anyone else who has had this
issue in the past would be much appreciated. My last experience
with pool repairmen was horrid so I want to be more prepared
before I call out someone else. I'm in Downingtown , Pennsylvania.
If anyone knows of a qualified and respected pool repair person here,
please send me that information as well.
Mariza

Mariza,
At 500 sq ft that works out to about 300 gallons per inch. Need to know what kind of a pool. Liner or what and I asume it's an in-ground? Let us know. There are a bunch of things to do to eliminate common leak points. Start by getting a better idea of the leak rate over time. It helps to measure water depth accurately every so often so you can determine if the leak rate changes with depth. That may point to a suspect area like the skimmer or returns or something else. You can make an accurate measurement with a ruler referencing to some known point like a specific spot on a step, skimmer plate or even the bottom at the same point. For example if you find one day you lost 300 gallons and 2 days later that decreased to 100 gallons, the water surface level is close to the leak. If no change then the leak is deeper. We'll get more detailed as we go on.
Al
BYW: I did a lot of experimenting a few years ago finding my leak which turned out to be at the deep end. About 50 gal per hour. Also developed a neat way to lay a good deep end patch. Vinyl lined IG pool.

Also try to measure the rate of leakage with the pump running versus without it running. If there is no loss when the pump is not running it will tell you that the leak is most likely in one of the lines.

I have gone "leak hunting" with a small squeeze-type plastic bottle filled with food coloring/water and a scuba mask.

With the pump off and the water relatively still, work your way around the sides squirting a few 'clouds' of color into the water, and watch to see if it tends to move. It'll be very visible if you get close to a leak.