Kyle's 20 Gallon Long

Well, we moved back in July and haven't had a chance to do anything or stock it at all. So its been a very boring tank with rocks. But I have had some good coralline growth (speaking of which, I need to clean my tank) and nothing really negative. My fanworms are gone, but now I have these weird little white spots. Ill get a pic.

But I do have a new buddy! I've been trying to get a pink-streaked wrasse in at my LFS, but to no avail. I got tired of being patient (after about 4 months of waiting) and got a yellow clown goby who is acclimating as we speak.
He was aweful happy in the store, but he's been patient and is perching while getting dripped.
Thanks Mitch. I guess it looks like either a fungal mat (no idea where it would've come from) or a sponge. Erin, they've been there long enough that I doubt they're eggs, but I suppose its a possibility. Ill try to clean up a little tonight and get a good picture.
So I was just at my LFS and they had a fighting conch. My research said 3-4" max and they should get along with everything pretty good. I asked and she said they've been really available so I shouldn't have a problem getting one in a week. What do yall think?

They also alwys have green mandarins and she said most of them eat frozen. If I can watch one eat in the next few weeks (gotta wait since I just added a fish last weekend), do yall think one would be okay in a 20?
A conch would be a nice pickup for your CUC, I've been waiting for one to come in for awhile.

I'm no mandarin expert but I think as long as it's eating frozen foods it should be fine in a 20.