[Molch]

I dunno, that's a lots of variables, but my guess would be the filter. These are pond-type newts and they can easily get weirded out by any kind of current.

I'd try without - you really don't need a filter. If you have good dense growth of live plants (which the newts love, btw) and turkey-baster up leftovers with occasional partial water changes, then your water quality will be okay.

I use a sponge filter in many of my tanks - t creates a slow bubble much like an open air hose and hasn't bothered any of my newts.