7 Best Plants for Aquaponics Fish Tanks in Australia

Pothos is the plant most people mean when they say aquaponics on a fish tank. Aquarium Co-Op says it reduces nitrate and algae, survives very low light and grows long roots that fish swim through. Aquafy sells two cuttings for $11.95 and stresses that only the roots go in the tank, because submerged leaves rot.

The trade-off is that it feeds nothing: it is a filter plant, not a food crop. It is also toxic to cats and dogs if chewed, though Aquarium Co-Op says it found no reports of harm to aquarium fish. Wash the roots well first, since Aquarium Co-Op warns to remove dirt and fertiliser. Compared with basil below, it needs almost no light management.

Mint suits aquaponics because it wants constant moisture. Bunnings describes a spreading perennial that likes cool, moist positions and partial shade, and Heritage Hydroponics lists mint for its small Penn-Plax systems. Bunnings also says mint grows in full sun through to heavy shade, which makes it forgiving of a dim kitchen bench. A 125 mm pot is $8.14.

The catch is spread. Bunnings warns mint runs into areas where you do not want it, so give it its own space and tip prune it. Roots that reach the water grow thick and can crowd a small planter. Against basil below, mint is far tougher, but it does not tolerate being left to itself.

Basil is the most productive herb on a fish tank, but it is also the fussiest about conditions. Go Green Aquaponics gives a pH of 5.5 to 6.5, a temperature of 18 to 29 C, 6 to 8 hours of light and a harvest 25 days after germination. It also says not to remove more than a third of the plant when picking. A 125 mm pot is $8.14 at Bunnings, which describes it as frost-sensitive.

That pH range is the problem. A tank held near pH 7 for most fish sits above basil’s range, so it may yellow. Frost matters too if you place the tank on a cold Canberra or Hobart windowsill in winter. Compared with mint above, basil pays better in the kitchen but demands more light and warmer rooms.

Watercress fits the fish tank idea better than most crops, since it lives with its roots in water. Go Green Aquaponics gives a pH of 6.6 to 7.5 and an ideal temperature of 10 to 16 C, which is cool for most tropical tanks. Bunnings says it suits all Australian climates and is ready 8 to 10 weeks from sowing, and Mr Fothergill’s Aqua watercress seeds are $4.80.

Two cautions apply. Bunnings warns watercress will not tolerate stagnant water, which can cause root rot, so the water needs to move. It also says not to forage wild watercress, especially near livestock, because of the risk of liver fluke. Harvest before it flowers, as Bunnings says flowering changes the flavour. Versus lettuce below, it is tougher but needs cooler water.

Lettuce is the classic aquaponics crop and it grows fast. Bunnings says it likes cool temperatures and partial shade, with 4 to 6 hours of sun a day, and seeds germinate in about seven days. A Green Mignonette punnet is $4.88, and Bunnings suggests planting a new row every fortnight for a steady supply.

Heat is the enemy. Bunnings warns that soil drying out can cause lettuce to bolt or turn bitter, and warm water does the same, so a January heatwave in Adelaide or Perth will wreck a tank-top crop. It suits winter and spring best. Its shallow roots also need more support than a hanging holder can give. Compared with watercress, lettuce is more familiar but far less tolerant of warmth.

The peace lily is a shade-tolerant houseplant that Heritage Hydroponics lists for its small aquaponic tank sets. Bunnings sells a 140 mm plant at $17.40 and describes lush dark green foliage with white flowers, growing in filtered light. That makes it a decent choice for a dim living room where basil would sulk.

Evidence is thinner here. I found no aquaponics owner report or independent test, only seller and product-set listings. The Bunnings listing does not state pet safety, so check before placing one near cats or dogs. It is also the most expensive plant on this list. Against pothos, it looks tidier, but it does not spread or trail.

Lucky bamboo grows in water with no soil, so it suits the smallest setups. Aquafy sells a rooted cutting of at least 15 to 20 cm for $9.95 and says it tolerates light shade and indirect sun, growing larger in bright light. Heritage Hydroponics lists it for the smallest Penn-Plax unit, a 0.5 gallon (about 1.9 litre) tank.

Aquafy also warns that tap water chemicals can burn its stalks, so use filtered water and change it weekly, which is at odds with a tank full of dechlorinated water and fish. Treat that advice with care, and watch the tips for browning. It absorbs little compared with basil or mint. Against pothos, it costs less but does little for the water.