Stocking a New 120-Gallon Pond: Koi, Plants & Snails

New 120-gal pond with filter/waterfall. Want 2–3 young koi, but worry they’ll eat plants. Also considering snails for waste. Plan to expand to 700 gal later.

Koi in 120 Gal? Not Recommended.

• Koi grow 24–36 inches. 120 gal is a temporary nursery only.
• Even 3 koi in 700 gal is pushing it (ideal: 250+ gal/koi).
• Start with **goldfish** (comets, shubunkins, sarasa). They stay smaller, tolerate crowding better, and are cheaper.

Plants That Survive Koi

• Floating: Water hyacinth, water lettuce—koi eat roots (cheap snack), plants multiply fast.
• Protected Lilies: Plant in baskets topped with 2" gravel + floating plant protector ring.
• Marginals in Baskets: Iris, pickerelweed, rushes—gravel cap deters rooting.

Skip Snails

• Non-native snails escape, become garden pests.
• Use a solids-handling pump or pond vacuum for detritus.
• Native snails will colonize naturally if conditions suit them.

Expansion Plan

When upsizing to 700+ gal: upgrade filtration (skimmer + biofalls), add bottom drain, increase depth to 3+ ft. Then consider 3–4 koi.