Elsie,
1" per month I doubt you would ever find a leak with dye. I had a leak of about 50 GPM (yes, minute) a few years ago and probably lost 10,000 gal before I found and patched the problem. Water table is usually high here and what water leaked out just went somewhere without washing away anything. My slits were at the deep end where the bottom transitions to the walls. I'd just let it go and start a record of accurate loss measurements.
Al