Should we go back to an undergravel filter?


Neale Monks gives his advice to a reader who is concerned about his elderly mother struggling with her community tank, and wonders whether it's worth going back to basics with airpump-driven undergravel filter.

Q) My 80-year-old mother is struggling with her 75cm community tank as she becomes less mobile, but she loves her fish. Things like taking filters apart to clean them are particularly tricky for her with her arthritic fingers. We are going to give the tank an overhaul for her in a week or two and wondered if she would be better off going back to basics with an airpump-driven undergravel filter in terms of ease of maintenance. What do you think? The tank is only lightly stocked with a few basic tetras, barbs and corys.


A) NEALE MONKS REPLIES: Undergravel filters often get a bad press these days, but they are low-maintenance and generally reliable once up-and-running. They do struggle a bit with messy fish like cichlids and plecs, but if you’re keeping the usual small community fish, undergravel filters can do the job well.

However, they do have some limitations. They are arguably incompatible with plants. Floating plants and plants attached to wood or rocks (what we call epiphytic plants) are fine, but plants with roots in substrates tend to struggle. Some species will adapt, particularly those like Vallisneria that absorb most of their nutrients from the water column and if started in a plant pot filled with rock wool, don’t really care about very much else beyond adequate lighting. Undergravel filters limit your range of substrate types to essentially plain gravel, and that gravel needs to be laid down flat, not sloped, because water will tend to be drawn through the shallowest depth of substrate and bypasses everything else. You also have to avoid creating dead spots underneath rocks or bogwood roots by limiting the use of these popular decorative materials. On top of that, they aren’t ideal for fish such as Corydoras that like to burrow, and these catfish are much more prone to getting their barbels damaged by gravel than sand. Stressed and damaged fish are more likely to become sick, adding another level of work.

But undergravels are quite easy to maintain. Siphoning the surface periodically should remove solid waste, and if done regularly, the risk of the gravel becoming thick with detritus can be avoided for the most part. You can often get away with stirring the substrate once a year, if the tank isn’t overstocked and solid waste is siphoned out regularly.

But my personal pick for very low maintenance would be a sponge filter. Maintenance is little more than removing the sponge and squeezing if necessary to release any solid waste. While the squeezing part might be hard with arthritic fingers, there might be workarounds, such as putting the sponge on the bottom of the sink and simply pressing down with something solid but easier to grip. Sponge filters do a really good job of managing water quality, hosting plenty of the beneficial bacteria that we rely upon for biological filtration. Small fish will also peck away at the algae and infusoria that grow on the surfaces of sponge filters, a useful bonus if you’re breeding things like shrimps and livebearers. The downside is their perceived lack of attractiveness, but with a bit of imagination they can be obscured with vertical rocks, tall plants, or bogwood roots.

Top tip

If elderly friends or relatives are unable to clean their tank, try combining your visits with a spot of tank maintenance.