From my experience and from what others have told me (including a breeder), ACFs do not like their water being disturbed by filters. Something about the current it makes. I have also read on another website that the Whisper filter is the best one to use with them.

Personally, in my 3 years having the couple I have not used a filter at all. I did get eggs from them but nothing came of them. I actually think they were too immature to be producing.

I plan on getting an underwater filter which does not move the water too much but I will remove it if I see anything unusual from them. I do think the filter is what caused the behavior you saw.