Or, you could put in a small tank or even a raceway under your main tank. Use it to actually culture aiptasias. Before you start throwing rotten fruit at me, aiptasias are useful as filter feeders if they are kept in the right places. Put them in the first section of the sump or in a raceway above the sump. All the water going down will pass through all those tentacles which will remove lots of waste particles from it. This not only increases the efficiency of your filter, but will provide a food source for your berghia. Once the main tank is cleared of them, you can pull a small rock out of the sump with some aiptasias on it and put it back in the main tank for the berghias to eat. Since they will be muching on them, there is little danger of the aiptasias spreading out of control. Just a thought.