Adding: we really want to put koi in but won't until we get the water into good shape.

First of all, water that may not look that great to us can be perfectly fine for the fish. You have a 9000 gallon pond and a filter rated for 5000 gallons???? I think that's your first clue of where to start. We'll get plenty of DOC's in our pond...all the result of those FF....but it goes away within a day or three. However, I'm running sufficient "biofilter" capacity to easily handle double the volume and fish load/feeding load. Most of the commercial applications I've seen are significantly overrated by the manufacturer in terms of capacity. You can always add a parallel system without having to tear out the existing system. While activate carbon would temporarily help with your DOC problem (as discussed elsewhere) I think you should look to a longer term solution....most likely by adding additional filter capacity.
---David

Right off the bat I'd say your filtration is inadequate, and you may have a lot of dead plant material rotting in there, which is bad for water quality. Generally your turnover (amount of water going through filtration system) for 9K gallons should be at least 4500 g/hr. More is better.

You need bottom drains and serious filtration for Koi. Koi are very dirty fish and even with no koi your pond doesn't sound very good right now. They are a big step up from goldies so get your pond right first and talk to koi people before getting even one koi.

Filtration consists of:

--mechanical (for fish poop, leaves, etc)

--biological (a place for a large number of ammonia andnitrite eating microorganisms to grow and remove impurities from the water)

--fines (a bead or sand/gravel--one for ponds, not a pool type--filter for removing tiny particles that the mechanical filter doesn't get, such as dead algae)

--UV (to kill off floating algae that green up the water)

Although some filters can provide more than one type of filtration, they are all best at one particular job. A separate mechanism for each phase is a good idea.

In addition to filtration, plenty of aeration, especially in warm weather. Warm water holds less oxygen then cold. A foam fractionator is a plus, but if the mechanical filter is highly effective, a foam fractionator can be necessary.

Start reading and researching. There's a lot of information out there, much of it contradictory! You have to keep reading and learning to know what is going to work for you. Joining a koi or pond club is also a great way to learn. You can meet some very experienced people who will not agree with each other on how to do things. But learning from them why they do what they do and what their knowledge is based on is enlightening.

The more you know, the more satisfaction you'll get from your pond and the healthier it will be.

Thank you both for your advice. I think you are both right -- we need to get another filter for sure.

Of course best would be to outfit the ex-pool with top quality filters and use the existing plumbing and all, but the costs are really too much for us in this economy.

I do not care if my pond is pleasing enough to the human eye for a spread in Architecture Digest. If the fish would be happy and healthy and we could see them, we'd be happy.

I am doing a ton of research on koi, from online and books and koi people. I am learning so much. I know I have to wait to get even one fish until everything is great for them here. But I want that day to come soon.

I am also a little scared of some koi experts because I do not know when what they advise is overkill BS and what is essential. Doctors often CYA and I know how to go around them and think for myself when to obey them and when not to. But with fish ponds, I am not knowledgeable enough to make that call. We can't afford to get sucked into a ton of expensive things that are NOT necessary.

I would also like simple and natural before complicated and artificial. I don't really know whom to listen to.