My pool was up for 2 years and it started to develop little dips here and there. We put 1" foam (pink stuff) under it when we put it up. I took it down before winter this year and getting ready to put it back up. The ground is completely level, there was no more than a 1/8 inch difference in the water level all the way around. For the areas where where the dips are at should i use sand or topsoil to re-level keeping in mind there will be foam board on top of it. There would be no more than 1/8-1/2" of material added. Also should the foam board be replaced?