Depending on the size of your pool and how fast it leaks. First check for any wet spots between the pool and equipment. If you have none and it doesn't take long to leak the water out, shut the equipment completely off and let it leak. Due to the law of gravity it will stop wherever the leak is. If the waterline drops below the light (If it has one) and or the jets, it has to be from the bottom drain.If it's from the jets or skimmer , it'll stop at that point and you can work with it starting from there. If it drops below your lowest visible fitting (jets,skimmer or light niche) on your side walls make sure you fill it back up and wait till you have a week or two of really hot weather so that any possible water under it will dry up and then drain it out to reseal your main drain on the floor level. Remember that if you have to much water under it, that water may cause it to shift or possibly even float much like an in ground spa.