Pete
Regarding your algae problem, I would first figure out why it's happening(old tubes or bulbs, dirty water, over feeding, ect...)
As for fighting conches, they work great at keeping the sand clean. I have four of them in my 27gl and I'm really happy with how well they house-clean. I would stick with "fighting" conches though, as others such as Queen or Strawberry conches can get too big in a small to medium sized tank. I also have two sand sifting Yellow Watchmen Gobbies that do a terrific job at keeping the sandbed clean
If you have trouble finding them on the Isl. then try Tim at Seacare(listed at the right of the page). Tim usually has a good selection of conches and sizes to choose from.
Goodluck
cheers, Rich