Green water can persist for up to three weeks after fish have been introduced. After around 5 or 6 weeks, the water will have cleared up on its own.
In the worst event, some of your fish may perish within 24 hours; but, if you have an air pump (which is recommended for all fishponds!), your fish will have a far better chance of survival.
It's possible the pond was built poorly or has a low clay concentration. Applying bentonite successfully requires compacting the soil with a vibrating roller. A geomembrane liner may be needed to keep water in ponds with particularly poor soils.
Every week, you should replace around 10 percent of the water in your garden pond. Check for contaminants with water quality testing to ensure your pond's water remains healthy. Try switching out 15–20% extra water if there are problems with the water's quality. Within a few weeks, you'll know exactly what your pond needs to thrive.