they should be just fine but i think its WAY safer to put in LR rubble instead of the bioballs. i have LR rubble in my 12 gal nano and my water quality has been perfect(i dunno if its just luck or the 10% weekly h2o changes)its up to you, people will tell you bioballs are horrible but theyre really not. they are a little risky in such a small system like the nano, thats why i think natural filtration from LR rubble is the best and easy.