This study aimed at understanding the processes resulting from air bubbling agitation & evaluating the performance of seaweed biofilters under culture regimes that do not use electricity for agitation. Agitation by only water exchange & simulated tidal variation in water levels gave biofiltration performances that did not differ from aerated systems. In an irrigation regime nutrient removal rates were not significantly different between the irrigation treatment & the control. Biomass yield, however, was different. Gravity generated water flow regime gave higher nutrient removal rates, seaweed biomass & protein contents in the treatment. It shows that seaweeds can perform efficiently as biofilters under low energy culture regimes that induce water movement for agitation of seaweeds without aeration as long as the biofilters are kept wet even if not submerged in water. The effect of biofilter air-agitation is not directly related to photosynthesis & carbon uptake, but to diffusion & uptake of other nutrients. Therefore, once nutrient concentrations are high enough aeration per se is not essential for effective biofiltration at least not with the most effective biofilter Ulva.