Biofiltration low impact designs (LID) such as raingardens are proven Stormwater treatment technologies. However, with Auckland and other cities of New Zealand witnessing increasingly high density developments, the land required for such traditional LID is not readily available. While green roofs are a possible LID alternative, in high density developments their suitability depends on the angle or pitch of the roofs. Suspended raingardens can be an ideal LID alternative for urban environments, providing a runoff treatment without needing land space. This is a multi-stage research project aimed at creating a novel approach to stormwater treatment in urban environments. The first stage of this research is focused on finding suitable lightweight media for suspended raingardens. To ensure that this new approach is reasonably equivalent to the treatment efficiencies of conventional practices, we tested different light-weight media compositions with densities in the order of 350 kg/m3 in the laboratory. Our trials were batch experiments focused on assessing their efficacy of removing total suspended solids (TSS) and dissolved metals: lead (Pb), zinc (Zn) and copper (Cu) from Stormwater runoff. The media we tested complied with TP10 regulations from Auckland Council in terms of TSS removal. The removal of all three heavy metals was significant too. However, we also encountered some practical challenges with the use of these media during our experimental runs. This paper discusses these findings and the viability of suspended raingardens as an effective stormwater treatment alternative for high density urban environments.