The Berghias you receive will vary in size but will be very close to what's seen in the picture.

How many do I need?
Up to 20g -> 4 Berghias
Up to 40g -> 6 Berghias
Up to 75g -> 7 Berghias
Up to 90g -> 9 Berghias
Up to 150g -> 10 Berghias
Up to 250g -> 15 Berghias

Direction on introducing Berghias into your aquarium:
1. After acclimating your Berghias by floating the container you receive them in, turn off all lights and power heads (so that fish will hide and don't see your new additions as food, also helps the Berghias to get a foot hold). There is no need to drip acclimate them unless your salinity is lower that 1.025.
2. Submerge the container you receive with the Berghias inside in the proximity of aiptasias. Never place Berghias directly right next to or on the aiptasias as they can sting or devour your Berghia. Berghias in hunting mode would know how to avoid being stung.
3. Leave lights and powerhead off for at least 15 minutes or until your berghias have left the container.

Additional Info:
The Berghias you purchase will not completely take care of your aiptasia problem; rather, it is the offspring from them that will eventually decimate your aiptasia population. Berghias are small, and aiptasias are bigger. It takes numerous Berghias to devour one aiptasia. So please be patient. Berghias are also experts in disguise and hiding. You will likely never see them again once placed in your tank. However if you're looking hard enough, you may find them crawling on the glass at night, or dwelling under a rock when you re-aquascape. You may even find egg clusters on your glass in the shape of a spiral.