first off, that red algae is not algae at all. It is a bacteria that forms primarily in newer systems, It is not good to have, although it really wont harm your inhabitants. It is very ugly however, and grows very quickly. and I'm sure you didn't go through all the trouble of a salt or reef aquarium to have this nuissance going on. On my first reef tank, it actually went away over about a period of a month or so. this doesn't mormally happen. I'm assuming you don't have any corals yet, so now would be the best time to take care of this, as all corals and most inverts like anenomes are very sensitive to water treatments. Fortunatly there is an easy fix. the product.....Ultra Life Red Slime Remover....should be a product your local store carries or can get you. I have used this product with success. This particular brand is supposed to be reef and live rock safe as well as crabs and snails and such. Get this product if you wish to take care of this problematic bacteria and rid yourself of it now. I would only use maybe a little more than 2/3 of the recomended dosage, give it a few days, and see how it goes. it should clear up in 24 - 48 hours. one more treatment may be necessary. You will be amazed at the results. It may temporarily tint the water yellow, but that will go away. wait a few more days, and then I would do a 20 percent water change. DON"T GET ME WRONG, I am always against adding any foreign chemicals or treatments to the water, but this one seemed to work for me when I really needed it, and now I am slime free and my tank looks great!
As far as sifting organisms, I would definatly suggest sand sifting stars, maybe 2 or 3 per hundred gallons, not sure how big your tank is, but two would be much better than one. this little creature, does an amazing job of turn over and aerating the sand. A black sea cucumber is also a great speciman for such duties. He will consume sand all day everyday, and defecate clean sand! very weird, but he does a great job at cleaning the sand as well. and your ten nasurius snails should do wonderfully also. I have all three of these types of creatures and they do a great job of turning and cleaning the sand, especially the starfish. Let me know if you have any other questions, I can help. good luck and happy marine keeping, Neal in Grover Beach, CA.