Purpleish Algae, Unknown creature?

Hi all,

I have couple questions, really appreciate it with expert answers?

First, is purpleish algae good or bad?
I have a nano cube 12 gal. I've had it for over 3 years. I have one damsel, one hermit crab, about 1 inch thick of live sand, about 8-10 lbs of live rock, alot of white starfish size from 1/16 - 1/2 in (literally alot of starfish), and one Unknown creature.
Here is my story:
I started up this tank step-by-step. bought some live sand and live rock, let it run, when it's suitable, add fish and etc (no starfish or unknown creature). One day, my friend's friend closed his pet store and asked me to come and get whatever left. I came and of course they got everything out already, except some junk. But I managed to have some 2-4 lbs live rocks, and put them in my tank. First, it was just normal like before, but after about 4-6 months, I noticed there are some starfish, and after couple months later, there are more starfish than ever. but they only come out when there is no light, and they hide away when I turn on the light.
But then there is one or two creature I don't know what it is, and it hides in rock when light turns on also. the only thing I can see before I turn on the light is its long smooth tentacle just reach out about an inch, never see its body (and just wonder if it has a body). I don't think it's a starfish, because starfish has 5 tentacles and this one has only 1 or 2 maybe.

Really appreciate your feedback or comments.

Thanks

Does the tentacle look like a starfish leg? It's possible it's a brittle or serpent star in the rocks. But really, it could be anything without a picture I can't be sure.

As for the purple algae, is it hard or slimy? Slimy is bad, that's cyanobacteria, or red slime algae. Hard is good, that's coralline algae.

Thanks Bifferwine.

I think it's slimy, is there anyway to treat it?
About the unknown creature, i don't know how the picture comes out, because it has only one leg extended out to 1/2-1 inch long, I don't even see the body at all, and when light is on, it hides in rock. but i'll try to take some pics.

You should treat it like any other algae -- improve your water quality. Reduce phosphates by running some sort of phosphate removal media like PhosBan or PhosGuard. Don't overfeed your tank, and only feed frozen foods; not flake or pellets, which contain ash and can lead to algae problems. Only use RODI water, not tap water. Do regular water changes (10 to 20% weekly). Reducing the amount of time you have your lights on may also help, as will increasing circulation in the area that the cyano is showing up. It has a hard time establishing itself in areas of high flow.

This is the only thing i can picture in my head. Is it this:

Thanks Cumminz,

The pics you're showing is starfish. Yes, my tanks has alot of them but are white. I'll try to take some pics of that unknown sea creature (unseen body, only see one leg extended out, maybe a pseudo leg or something). I'll post pics later. Thanks

The starfish that you have tons of in your tank are probably asterina stars. Google those and see if that's what you have.

I just checked out asterina stars. Seem like they have shorter tentacles compare to the pic above. Starfish in my tank are white and has long tentacles. I'll try to take some pics tonight. Thanks Bifferwine.

If yours have longer, skinnier legs, they are probably baby brittle or serpent stars, which are good to have.

The unknown creature is probably either a serpent or brittle. You will only usually see 1 leg that sticks out and its at night time usually. You can hit them with a flash light at night and they suck back into the rock. Im not a bettin man but I would bet its some type of star. Goodluck!!!

I'm think the critter is probably small brittle stars too.Their safe.Theres hundreds in my tank.