I would consider increasing water circulation via additional powerhead and airstone. Think of your 10g/55gal tanks as a fuel cell that needs to be "wound up" otherwise redox reactions are not in balance.
The aponos could also not be getting enough PAR light. I would recommend full spectrum bulbs or try 2 23W 6500K CFLs. They are small and currently far from critical PAR light. Mine flourished in fast current and 14W full spectrum fluorescent bulbs