Replacing substrate is really buggery. You also pick up a lot of dirty and crud when you do it. I had a miserable time trying to get up my coral sand, but i'm sure with pebbles it'll be alright. If you need to cut your eco complete get some PFS and lay it under the eco complete. Or hop on down to the home depot and pick out some PURE vermiculite, make sure it's PURE, and use that. (it's the same exact stuff as eco-complete, well it doesthe exact same thing that is, it has a very high Cation Exchange capacity) You would have to cover the vermiculite though, it clouds water and does wacky things when exposed.