I am not familiar with "rock beauty anemone" for a name... is this a rock anemone? Growth rate and final size will be best determined by an accurate identification of the species. Can you post a pic? I'm familiar with most of the common anemones available in the fish trade, and can usually identify one with a good picture.
As for the tank its in, even the smaller species of anemone will outgrow a 5 1/2 gallon tank quite soon. What kind of foods are you offering and how often? What other animals are in the tank? What are water params?

 

First guess it's a nuisance majano anemone.

Next guess is even worse, Aptasia, AKA rock anemone, glass anemone.

 

There is a species of anemone that is termed "rock anemone" that is not a troublesome anemone, but rather, a decorative and fun animal. These are also a bit easier to keep than most of the other anemones. As stated earlier, a picture would surely help.

 

the anenome is in the top left, that was prob 3 weeks after i got him. i feed him marine food, frozen krill plus anything he eats out of water. i also saw him catch a live shrimp that i got from the ocean when i went to get pods. there are a blue legg hermit and a crimson, 2 turbo snails, a oscellarious clown fish and a coral banded shrimp. ph is just under 8, nitrite and amonia 0, and nitrate kept below 15.

 

That appears to be what I was referring to as "rock anemone". They can get quite large, so I wouldn't keep it in the 5.5 gallon for a long time... nor would I suggest that the mandarin stay in a 5.5 gallon, either. Anything under 55 gallons with a mandarin is more or less a death sentence. They are difficult feeders and very shy. To find enough food to sustain it longterm, because they need to eat almost constantly, under 55 gallons is very temporary. Waste levels will also play a part with the fish because they are extremely sensitive to waste levels, and as they grow, the waste increases.
I would get the pH level up to at least 8.2 - 8.5 to keep everything healthy, also. Do you know your calcium levels? This, also, will be very important.
Here are some accurate links that may help you:
http://www.liveaquaria.com/product/prod_Display.cfm?pCatId=1704
http://www.reefcorner.com/SpecimenSheets/mandarinfish.htm
http://en.wikipedia.org/wiki/Dragonet

 

thanx, the mandarin was just to be in there temporarily, he was in such bad shape when we got him there wasn't really muchhope for him. we just thought we'ld try to get him somewhere with lots of food, no competition and noone to bother him. then if he actually recovered we would move him into a better home. what would u suggest to bring up ph? fro what i read it was best not to try to change ur ph alot incase u had to do an emergency water change for some reason

 

what would u suggest to bring up ph? fro what i read it was best not to try to change ur ph alot incase u had to do an emergency water change for some reason

Use crushed oysters to raise the pH.

 

Usually your ph will swing through out the day. Test your PH in the morning, afternoon, and evening. You want to see when it is the highest and go from there.

 

Once you know where you're at with pH, adding a small pouch of crushed coral to your filter should be enough to bring it up where it needs to be. You can either use a mesh bag or even a nylon stocking that is then tied off. Rinse the coral before you put it into the filter, and simply add to it as it breaks down over time. You'll want to keep regular monitor of your calcium and pH after that to be sure they stay stable.