I have 2 Platys in an Eheim Aquastyle aquarium. Both have swam up behind the filter and appeared to be stuck between filter and glass? Is this normal or is something wrong with them? The filter has a waterfall kind of return and the filter suction is on the front and its a pretty calm filtration so they don't seem to be getting sucked behind it? I'm afraid they will be stuck & I won't be home to get them out?? Any advise??