Freshwater issue

[Buddha51]

So I changed my water to 80%. The filter is clean and this is my issue after WC. PLEASE HELP.

 

[Brymac1]

Algae bloom. Either completely black out the tank for 5-7 days or run a UV sterilizer.

 

[nereefpat]

Is that tank good and cycled with no ammonia reading?

Koi are huge waste producers.

 

[DrZoidburg]

Did you use city tap water, or well water? These can have enough nutrients in them to cause this. Mentioned above is a good option. Also could get a few freshwater clams. They filter loads of water.

 

[steven m]

When I worked in fish stores I use to see people with the same problem. It’s and algae bloom like @Brymac1 stated before. Most commonly caused by running the lights on 24/7. Or for an extended period of time. Most likely the tank is being over fed because koi would eat like they’ve never seen food before. I would recommend getting a canister filter filled with bio media and filter pads, fluval is a good choice and do 25% water changes a week and keep the lights off for most of the day.