How long do berghia take to get rid of aiptasia?
It depends on how many aiptasia you have and how many berghia you add. Our 16 gallon, with about six aiptasia and four berghia, was clear in about a week. A bigger tank or a heavier aiptasia problem can take anywhere from a few weeks to a few months.
Our timeline
Our 16 gallon had about six aiptasia when we added four berghia. We saw the berghia the first night and then never again, but one by one the aiptasia disappeared. It took about a week, and we haven't seen one in that tank since.
That was a small tank with a small problem, though, so I wouldn't expect a week in a big tank that's covered in aiptasia.
What changes how long it takes
The biggest thing is how many berghia you have for how many aiptasia. More berghia means more mouths. Rockwork matters too, because the more hiding spots there are, the longer it takes them to find every last aiptasia. And anything that picks off berghia, like certain tankmates or a hungry pump intake, slows things down (here's what we know about tankmates).
How to tell it's working
Watch the aiptasia, not the berghia. Pick one or two aiptasia you can see easily and check on them every day. If they're shrinking or disappearing, your berghia are working, even if you never see them (we never saw ours).
How many to start with
Starting with enough berghia is the easiest way to keep the timeline short.
And if you're still comparing options, here's how to get rid of aiptasia (what we tried, what we skipped, and what worked).