Some systems run sir stones others run with no flow just regular water changes seen some with fans from remote control boats and mini water pumps and even mini external pumps and seen 2 systems that used gravity piping for flow
Lots of different options but common theme with most of the pico systems is the frustration level for every one that works there are 8 failures.
Good luck in your endeavour and hope it turns out great for you
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 My aquarium is nothing but a smorgasbord for my cats.....
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