Hello and welcome to the site. I know very little about changing water conditions except that aeration is always helpful but doesn't seem likely in your case. If you want a clearer BOW do not put in Koi. they root around in the bottom and just constantly stir it up. Catfish will do so to some extent but are at least catchable. Koi are difficult to fish for or at least were for me, I ended up shootin or spearin them out. I only put in six and it took a long time getting rid of em. If ya put in some predators you will need forage for them unless you can feed yr around. Might want to consider HSB and Bluntnose minnows, Spotfin shiners and maybe GSH. Good luck and do not hesitate to ask ?s. Guys much smarter than I will chime in.
