New 300-Gal Pond: Green Water, Feeder Fish, and Koi

300-Gal Pond, Green Water, 2 Koi — Fix the Basics

3 weeks, feeder fish + 2 koi, pea-soup green, cleaning filter daily. Classic new pond + undersized filter + too many fish.

Immediate Fixes

• Stop daily filter cleaning — destroys bacteria.
• Upgrade filter or wrap pump intake with filter media in a basket.
• Add LOTS of plants (floaters, oxygenators, marginals).
• Barley straw + beneficial bacteria (Microbe-Lift).
• Reduce fish — 300 gal is too small for koi long-term.

Koi Reality

1000 gal first koi + 100 gal each. Your 300 gal = temporary only. Keep the 2 koi, add goldfish later.

Read Algae Control.