Get some shrimp. Since I got shrimp in my tank, 4 ghost shrimp, 2 amanos and 1 bamboo shrimp, my 20 gallon has been spotless. Sometimes pufffers will kill your shrimp, sometimes not. Buy some cheap ghost shrimp (usually 3/$1.00) and test it out. If the puffers leave them alone, pick up an amano or two.