I was walking by my tank and the room was pitch black and I heard splashing. I thought maybe a fish was trying to jump out so I flicked the light on. Didn't see any fish and then I heard it again coming from my filter! I looked and sure enough, there was a female Ancistrus sitting in the current of a HOB filter. I ran downstairs grabbed my camera and hoped it'd hang on. I managed to snapped two shots before it zipped back into the tank. This filter has a lid over the output so nothing can jump out unlike the Aquaclears. The filter used to have a bio-wheel but I took it off.
Haha, yea danios are fun to contain. When they spawn it's like rapid fire jumping out.
There's no media in the filter except a couple bags of biomax so I'm not overly concerned if they get in. Just have to make sure they can get out. =P I'll have to check it regularly.
My baby Ancistrus climb inside the internal power filter- I used to put a micromesh piece of angling keep-net over the filter to keep them out, but I've given up even trying as most of them seem to come to no harm. Changing the filter seems to have stopped all bar a couple of intrepid ones- with the Fluval 3+ there were often over 30 of them in the filter when I took it out for maintenance...