I dont remember how long your systems been running.So just keep a very close eye on your peremeters and be ready to do water changes just in case.
If the anemone had eattin the day before,it could be just taking a crap.If its shrivled up then thats my guess.
How much light do you have?Even though bubble tips are the easiest anemones,they require a lot of light.No less than 9 watts per gallon.Nitrates will make them sick,nitrite and ammonia will kill them.
If it deflates and starts slimming,pull it out and smell it.If it makes you blow chunks,toss it.
Other wise,good luck with it.And wheres the dang pics?:D