That's exactly what Iv'e been doing for a good hour. carefully pulling out what I can and scrubbing with a tooth brush . Then it will be blast time ! I have an old penguin attached to a stick This really blasts the crud out /off the rock Grassy, I was also losing a lot of snails after a couple weeks. I started Slow dripping new snails for hours . 2 at least Maybe over kill but the snails seem to live for the long term.