Need help to decide what kind of clean up crew to get

[jojoandphia]

Ok so this is a long one...
I have a 55 gal tank that I have had for years with cc and bio-balls and I know that I need to change that to live sand so I got a new 29 gallon tank about 6 months ago and started it with live sand and live rock from my old tank. After about a month I got some new fish (cleaner clam, lawnmower blenny, yellow wrasse and a pinstripe wrasse). So about a week ago so almost 6 months after starting the tank I started noticing some grey to black stuff on top of the sand. So I did a water change and hoped that I was just over feeding so I cut back. Now everyday it has gotten worst so I guess I need to get a clean up crew or something.
After looking for awhile here I am thinking about getting 20 nassarius snails some for 55 gallon tank, a fighting conch, a sand sifting star fish, and a brittle star. What do you think? I was looking at the shrimp and crabs however I am concerned that they might fight with or hurt my current fish. Any help is must appreciated.

 

[snakeblitz33]

If you have crushed coral, I would definately not get a sandsifting starfish. What you have is a case of cyanobacteria. You can get cyanobacteria because of very low flow, causing a build up of detritus and decay. Another thing is that cyanobacteria colonizes because of high nutrience in the water.
Check your nitrates, change out your crushed coral with live sand. Do a few water changes.
Add some hermit crabs, nass snails, astrea snails, (I would stay away from conchs). Cleaner shrimp are really cool, especially if they set up a cleaning station for your fish.

 

[jojoandphia]

No I have live sand in the tank that has that stuff building up. Because of the sand I can't just siphon it out so should I try to grab it with my hand until I can get a crew? Or should I just move the sand over it? The sand bed is about 3 1/2 inches. I am not sure because all the things I have read say try not to disturb the sand if possible. I don't want it to affect my fish.

 

[scopus tang]

How deep is your sand bed? Regardless, you should be able to simply reach in, scoot the cyanobacteria together into a pile and scoop it out with your hand. Disturbing the sandbed is really only an issue if you have a deep sand bed.