interesting. i use a filter using sponges and wool whilst in use for my water feature and aids in the debris removal only. i wouldn't consider using it to actually "cleanse" the water because after one weeks use the media would become obsolete with my four toads. CARBON: any decent aquarist (filter user) would not utilise this has frequent water changes should be in place anyhow. CERAMIC: if after one weeks use and its pores gets covered by the residue from the toads, how can it do any nitrifying. anyone who has 2 or more toads will (and should) know how this slime builds up in the abode and needs to be addressed by a rigorous cleaning regime of the pool/water area. my point is, with such a small volume of water generally used by the "toadees" a filter does not replace the water changes that need performing regularly. on a larger scale, yes, then a filter would come into play as such a small load of residue could be tackled but the media would still need to be rinsed that often that...........well you know. and yes i know about media as i was a reef keeper for many a year. carbon, meh.