When I raised Koi as a hobby I used UV ( OK but lots of maintenance ) then went to ozone but that one bit more than a little in the wallet. You have two issues micro and organic requiring different solutions. Organics require a back flushing system which captures waste from the water then what to do with it is a real problem I ran it into a huge bio filter but I was small potato to commercial.

Then the regs! Hatcheries for years used a green die that killed off micro things but fed by the tablespoon rats could develop cancer but if you ever had green carpet you had it in your home. So EPA said change which sounds good but......the replacement? Formalin which is liquid but formaldehyde is the main active ingredient.

To be honest folks if the same standards that DOE in this state were applied to a city such as Seattle you would damn near have to abandon the city! You see fish do not vote, only a few in aquaculture, lots of votes in city, big big cost to urban folks and they vote. You figure out what happens next with this story.