Reviving a Neglected Koi Pond: Sludge Removal, Fish Rescue & Filter Install

Inherited koi pond: murky, 6" sludge, 15–20 healthy 8–10" fish, no filter. Draining halfway revealed fish — stop draining. Here's the rescue plan.

Emergency Fish Holding

1. Kiddie pool (100+ gal) in shade.
2. Fill with pond water — same temp, chemistry.
3. Add pump + air stone — circulation and O₂.
4. Net fish gently — move all to holding pool.
5. Cover pool — prevents jumping, herons.

Pond Cleanout

1. Drain completely — pump or siphon.
2. Remove sludge: Shovel, wet vac, or hire vacuum truck.
3. NO chemicals — scrub with water only. Rinse thoroughly.
4. Inspect liner — patch any holes.

System Install & Restart

1. Install pump + filter: Pressurized biofilter (e.g., OASE BioSmart) + UV clarifier.
2. Pump size: 2,000+ GPH for 2,000+ gal turnover.
3. Plumb bottom drain if possible — best for sludge prevention.
4. Refill + dechlorinate.
5. Acclimate fish: Gradually add new pond water to holding pool over 2 hrs until temp matches.
6. Return fish.
7. Run 24/7. Add bacteria starter.

Filter Selection

• Pressurized: Easy hide, backwash handle — good for retrofits.
• Gravity-fed: Better flow, needs elevation — ideal if building new.
• Must have: Mechanical (foam/matting) + biological (high-surface media) + UV.

Sludge is toxic. Fish survived by luck. Give them a filtered home — they've earned it.