I ditto tiller and others. Good advice from all so far. The only thing I would add about chemicals...is that there is one bottle of stuff you really should have, and that is a water treatment for Chlorine and Chlorimines. Chlorine is not that bad if you add less than 10-20% of your total amount at once. The fish can get Gill Burn if they play in the hose spray so put the hose in a area they can't get to. The chlorine will hurt your bacteria colonies in your bio filter but won't wipe em out. After a day or two contact with the air will dissipate the chlorine (it will go faster if you have an airator or waterfall). Chlorimines though are baaaad. They will never leave your pond without being treated with an additive. You can call your water company and see if they use chlorimines. If they do, then you need to get in the habit of using a neutralizer every water change. If they don't then you can get away without, unless you notice your plants being hurt by chlorine when you change the water. "Bad stuff" on the bottom are organic compounds like leaves, fish poop, dead fish etc. As it decomposes it will create a layer of mud called "muck". It's black and smells bad. If your pond ever has a sewer odor that's a sure sign that your muck has run amok and the fish are in danger. When this happens oxygen levels drop and you start getting brown algae and your water will look like rootbeer. Anaerobic bacteria start to go to work in the oxygen free environment. This is a fish death sentence. You should regularly scoop out the majority of the muck leaving as little as possible on the bottom after it settles back down. "Regularly" depends on your pond. More trees, dust, pollen, weaker filter etc mean you need to clean it up more or less than others. There is no rule about how often to clean. To clean out muck, you just need to scoop it out. You can do that by hand, with a bucket or shop vac. One thing I like is this little attachment that goes on the end of a garden hose. The flow of the hose water creates venturi suction that pushes the muck into a little nylon bag. Keep in mind that with any of these options you will stir up the muck and it will take a day or so to see improvement. If you do it regularly, the stirred up muck isn't a problem for the fish. But if you have a deep layer of it you might want to do what destany said above, and move the fish into a container for a bit (filled with pond water!) as all those bad compounds will be spiked during the clean. If your depth is closer to 3 feet I would still think about either getting rid of the goldfish (donate them to a pet store or other ponder) or the koi. With either 3 koi or 11 goldfish you have about the right fishload. But with both, you have about double what you will need in a year or so when they get big. If you are dead set on keeping all of them, you need to plan on losing some to stress or plan on getting a heavy duty biofilter and/or doing regular muck sweeping.

Yup, this is an ancient thread, but very helpful. I had to give up the pond eventually as we were starting a new house build and that summer the (really old) liner developed some big cracks due to age. Gave my two humongous koi to a local pond supply place and removed the pond. I figure the house will sell easier without something future owners may look at and think "high maintenance" (not that they're wrong, but...) and I want to ditch the old house fast when the time comes. I write this post simply to say to new pond builders: When you buy a pond liner, get a REALLY GOOD UV PROTECTED one that is mostly thick rubber, not plastic. I thought mine was thick enough but after 12 years or so, it started to wear out due to sun, get brittle and just start having problems. You drop a rock? Oops, hole! Now the pond area is just a plant area and all I have are memories of better pond days. I'll have a pond at the new place after things settle down and thanks to many posters here for all the info to help keep the water clear when that time comes!

For over 30 years I had a cement pond, triangular in shape, about 5 feet long which naturalized. Lots of lilies, water hyacinth and gold fish plus guppies. ocasionally added water, but it was in full sun; didn't have an algae problem. No filter, no special water treatment. This was in Southern California. It ended up with a dirt bottom because the lilies, fish waste, etc drifted to the bottom. Water was clear as a bell, lilies were colorful. Our koi pond on the other hand 25 feet away is filtered, treated, etc. and it turns completely green every so often. Koi love it but its much more work.

Thanks everyone for your advice and support. I hear we are in for more storms and heavy showers in the next couple of days Chippewacat, so keep your fingers crossed for me! Here is an update on the weekend's work. You know, my friend Gordon who is 81 and me at 71 are a bit too old for this kind of caper, but the work had to be done. On Saturday afternoon Gordon cleaned as much of the gunk and debris from the paving and shrubs as possible. Bless him, he made me stay indoors because the smell was really horrible! Then yesterday morning we started to empty the pond. I had tried to get the ammonia reading down by doing a partial water change on Friday but it was still dangerously high so needs must. At least I was able to save tap water by using the water being pumped out to hose down the paving. My poor fish weren't too happy at being placed in a polystyrene container about 2 foot square and ten inches deep, but they managed to survive. When there was not enough water left to be able to use the pump the really horrible work began. In Gordon's wellies I was passing bucket after bucket up to him to throw into the bushes. Unfortunately, it didn't occur to me that there could be fry lurking in the weed and murky water so I don't know how many were thrown to their certain deaths I found five when it got the stage of scooping up gunk and water with a large plastic jug I was so thrilled to know a) that my fish have spawned this year and b) that if the five survive, they will make up somewhat for the fish I lost. The final count was four found dead and three missing presumed dead. Sad to say that among them were three of my latest acquisitions - 2 golden orfe and a sarasa comet, sniff, sniff! Now I need to know how I should care for them. At present they are in a washing up bowl with a bit of weed for cover as I don't want to put them back in the pond till they are big enough to fend for themselves against the bigger fish. I tried to feed them with crushed fish food last night but there were no takers. Anyone know what I should be doing? After all the gunk had been removed - (and you wouldn't believe the stuff I found, cigarette ends being the less odious - I'm sure there must be someone in this area who cleans their ash trays by tipping them down the loo! Disgusting! and in my opinion panty liners should be banned) and the plants all sluiced down I used two of my waterbutts of rain water then tap water hosed in from a great height (to oxygenate the water a bit) to refill the pond. It was also treated with a dechlorinator and the grateful fish were placed once more in the home they had scarcely had time to become accustomed to before disaster overtook it. The new pond was only finished in April! We held a bucket under the waterfall and switched on the pump and filter - but very briefly because the water was so filthy it was obvious a major cleaning of the filter was necessary. By this time - 8pm and not yet had...