Your Haddoni spawned. What you need is to do a large amount of water change to remove the nutrients that introduced to your tank.
When I see my anemone spawn, I have many large anemones in my tank, I always try, if I can, to suck the water at the mouth of the anemone as (s)he spawned and remove the eggs and sperms as it come out. Doing this I can get rid of the nutrients without s doing as large water change once the spawn is over.
Depends on how small your tank water volume is, you may need to do a 75%+ of the water to remove the nutrients.
If you feed your anemone well, they have huge body mass invested in sperms and eggs. From what you wrote, you likely have a male. Sperms are like smoke coming our while eggs are larger, you can see individual eggs.