Does light make aiptasia grow faster? (And will turning off my lights kill it?)
Light does help aiptasia grow, because they have tiny algae living inside them that turn light into food. But turning your lights down won't get rid of them. Aiptasia can also live off food floating in the water, and your corals would suffer long before the aiptasia did.
Why your reef lights help aiptasia
Aiptasia have tiny algae living inside their bodies. The algae use light to make sugars, and they share those sugars with the aiptasia. It's the same kind of partnership a lot of reef corals have, which is why aiptasia love the exact conditions you set up for your corals.
Your reef tank is basically an aiptasia spa: bright light, warm water, and plenty of food floating around. That's a big part of why one aiptasia can turn into a lot of aiptasia so fast.
Will turning off my lights kill aiptasia?
Unfortunately, no. Aiptasia get energy two ways: from the algae inside them, and from catching food in the water. That second one lets them hang on even in dim spots, like the back of your rockwork or your sump. And turning your lights down would hurt your corals long before it hurt the aiptasia, since most corals depend on light the same way.
How we know aiptasia love light
We grow aiptasia on purpose to feed our berghia (the only thing berghia eat), so we've set up tanks to give aiptasia everything they want. That's small tank lights for 10 hours a day and water close to 80 degrees, and they grow. We haven't tested different lights against each other, so we can't tell you which light makes them grow fastest. But if your display tank has good reef lighting, you're giving your aiptasia what we give ours on purpose.
A quick look at the tanks where we grow aiptasia (starts at 6:46)
What actually got rid of it for us
In our 16 gallon, four berghia cleared about six aiptasia in about a week, and we haven't seen one since. Berghia eat aiptasia and nothing else, and they hunt down the ones hiding in the rockwork. Here's how to get rid of aiptasia (what we tried, what we skipped, and what worked).