They don't work well sideways because the water does not flow right through the entire filter. I use em in my QT
and med tanks all the time. Toss da cartridge and you're done! I usually keep one filter in my tanks for cycling QT
You may be better of with something like a duetto filter. It is made to be in several positions (bottom, sidedways, on the sides).
Otherwise the water side level has to be deep enough to cover it at least at at ipped angle with the up side mostly up or free floating ..
for some reason sideways makes it reallly crappy. And they ALL bubble oddly and sporadically.