Activated Carbon in Koi Pond: Clearing Tannins and Salt-Tolerant Lilies

Carbon Cloudiness Is Temporary

Fine carbon dust causes black cloudiness. It clears in 2–3 days as particles settle or are filtered. Run a polishing pad or filter floss to speed it up.

How Much Carbon?

1 lb per 1,000 gallons is a standard maintenance dose. For heavy tannins (redwood leachate), use 2–3 lbs in a mesh bag in high flow. Replace every 4–6 weeks.

Why Add Salt in Spring?

If it's for parasites, treat in a quarantine tank instead. Salt at 0.1–0.3% stresses lilies and marginals. Most hardy lilies tolerate *brief* 0.1% salt, but chronic exposure yellows leaves.

Salt-Tolerant Plants

• Lilies: 'Charlene Strawn', 'Joey Tomocik', 'Perry's Baby Red' (anecdotally more tolerant).
• Marginals: Cattails, bulrush, pickerelweed, iris, sweetflag.
• Submerged: Hornwort, anacharis, Vallisneria.

Better Approach

Fix the tannin source: seal the redwood trellis or divert runoff. Use carbon for polishing. Avoid routine salting—address specific issues (parasites, nitrite) with targeted treatments.