Clearing Green Water in a Small Patio Fountain

Fixing Pea-Soup Algae in a 24-Gallon Fountain

A 24-gallon patio fountain with 3 goldfish, 3 hours of direct sun, and a power filter developed thick green slime and pea-soup water. Barley peat extract worsened it. The system is too small for barley to work effectively—it needs volume and time to release beneficial compounds.

Immediate Action Plan

1. 50% Water Change: Siphon out green water, replace with dechlorinated water.
2. Add Algaefix (or similar EPA-registered algaecide): Dose precisely for 24 gallons. It kills suspended and attached algae fast.
3. Use a Flocculant/Clarifier: Clumps fine algae for filter removal. Run filter continuously.
4. Reduce Light: Move fountain to shadier spot or add floating plants (water lettuce, hyacinth) to shade 60%+ of surface.
5. Remove Barley Product: It's ineffective in tiny volumes and may add organics.

Long-Term Balance

• Limit fish to 1–2 small goldfish; 3 overloads a 24-gal system.
• Add submerged plants (anacharis, hornwort) to compete for nutrients.
• Clean filter media weekly in old pond water (not tap) to preserve bacteria.
• Feed sparingly—only what fish eat in 2 minutes, once daily.

Can You Keep the Fish?

Yes, if you stabilize the environment. Goldfish tolerate green water short-term, but chronic low oxygen and high ammonia will kill them. The above steps restore clarity and health within days.

Small fountains need proactive management—nature won't balance them alone.