Apologies for resurrecting such an old thread, especially as a newbie here, but I thought I may have an update that may prove useful to others.
We have just changed from Goldies to Tropical. Our tank is a Juwel Lido 120, and we have a school of ten Zebra Danios in there(with other fish too). Unfortunately, on day two some of the Danios got into the filter, so we released them. The next day I changed the poly pad and rinsed the filters in De-chlorinated water. Unfortunately, while I had the filters out these crazy Danios were swimming all around the filter head, I was worried some would get trapped in the filter case and be stuck under the sponges, but when it came to it I had to just put the sponges back. How would I know if there was one at the bottom or not? I did a head count of these mad little swimmers afterwards and could only find 9. We checked again later, and it was still 9. I was looking carefully and then I saw something move right in the corner of the tank, it was the Danio! It was stuck, vertical, in the tiny gap between the glass and the filter. I searched the internet for possible ways to free the poor little thing, but couldn't really find much except this is a known problem. We could see that he could change direction and swim about, and so we hoped he may move sideways in a bid for freedom.
Unfortunately it was not to be. After a few days, my wife and I couldn't take this much more, so she suggested getting a straw and sucking it out. We tried it, it didn't work. But then, I pushed the straw down further, and got a syringe from a JBL test kit and pulled water up into the syringe. I then lifted the straw, and put it in the tank. My wife blew the straw, and hey presto, one little zebra danio fishy back in the tank! We got some flakes and a treat of freeze dried brine shrimp in there pretty quick. He has been eating, and we hope that he may be OK. We will have to wait and see if he survives his ordeal. In the meantime, one of the others who was trapped in the filter perished, but all others are OK.
Knowing that this is a fairly common problem I wanted to pass on this method that we used to set the fish free.
I don't know why Juwel make these aquariums like this. Admittedly ours has been "modified" in as much as when our Goldie died, I emptied it out and wanted to give the filter case a good clean, so I pulled it out, not realising it wasn't like my old Fluval filter and was actually stuck to the glass! At the fish shop they sold me some Juwel Connexo, which I then used to fix the filter back, but it went back in exactly the same place, and I have read of this happening with a factory spec tank. I can't easily do the bead of silicone now either, as the tank is full up, and I don't really have access to another to house the fish, and I don't want to start it all from scratch again. I believe the risk is now low as the Cardinal Tetras and the rest of the danios are now too big to fit in the gap. I doubt the one little danio will want to repeat his experience!
Anyway, I hope this may prove helpful to somebody in the future.
