Goldfish Care Tips

A Free Monthly Resource For Goldfish Enthusiasts
September 2026
Issue #153

In This Issue
Watercress and Aquaponics

www.about-goldfish.com/

Watercress is an ideal plant for aquaponics setups because it grows quickly, needs little or no substrate, and tolerates its roots being in water.

Watercress and Aquaponics

Watercress in lily basket - very slow growing

To be fair, my attempts have been fairly average to poor, with one of my regular customers commenting on an earlier attempt, saying, “Well, that isn’t going to feed a family of four, is it?”

A tad harsh, I thought, but she was right.

What is Aquaponics?

Quick recap: aquaponics combines hydroponics (growing plants without soil) and aquaculture (raising fish).

Fish waste provides food for the plants, and by feeding on the waste, the plants maintain good water quality by reducing nitrates, or that’s the theory.

Why Watercress?

Several reasons;

• it grows fast
• it can tolerate its roots in water
• it doesn’t need strong sunlight
• it is low-growing, so it will fit under my mesh pond covers
• it has a long growing season
• it is considered a superfood
• it is easy to propagate.

All these attributes have proven to be correct except one: fast-growing.

I set up 6 ponds with water lily baskets and a little limestone for substrate.

I found a huge difference in growth rates, ranging from complete die-off to a reasonably lush result. But the best result was slow-growing.

I noticed that the best results were found where the filter uplift tube from my sponge filters was near the basket. The die-offs occurred where the basket was at the other end of the pond from the filter.

A New Plan

My thought was, if the watercress grows best when there is moving water close by, what would happen if water was pumped into the basket?

I decided to use a plastic planting tray suspended in the pond on hooks, as the lily baskets are a little fragile.

Watercress in tray

This setup forces the water to move across the tray through the watercress root ball before exiting back into the pond.

The results have been spectacular, with the watercress cascading out of the tray and into the pond, needing frequent harvests to keep it under control.

The nitrate level in the pond is 1-2 ppm (parts per million).

Why Not Use Aquatic Plants?

Aquatic plants can quickly take over a pond, or conversely, fail to thrive.

The test pond is in shadow during winter, and in early spring gets only morning sunlight, so aquatic plants aren’t really an option.

Having a long growing season, there really isn’t a problem with Autumn die-back. The watercress actually survived winter temperatures and being in shadow all day.

Also, the tray is easy to unclip and remove if I do want to clean out the pond or catch fish.

Conclusion

I concluded that because watercress is a gross (heavy) feeder, it wasn’t getting enough nutrients in the ponds, as they have low nitrate levels.

Watercress can be grown in soil as long as it isn’t allowed to dry out. Soil or potting mix would provide the nutrients it needs to grow quickly.

By pumping water into the tray directly from a filter outlet, it provides a continuous flow of nitrate-rich water across the root ball because, as we know, filters are nitrate-producing factories.

www.about-goldfish.com/

www.facebook.com/aboutgoldfish