Hi Arorules,
A fliter is a necessity if you intend for the ammonia produced by your fish to be converted to nitrite and then to nitrate that the plants can use.
Without a filter, the above process is almost impossible. A filter will also help you remove any water born particles that will clog up more delicate plants.
Also, If you are dosing CO2, using a bubble (air pump) will only be counter efficient cos, the air pump aerates the water thus causing you to lose CO2 via surface agitation.
Although I am sure a low mantenance 3 ft is possible with no filter and airpump, you have to be extra careful with managing your CO2 dosing ,water chemistry and bioload
Regards
Robin
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