Koi Fish and goldfish

Question
I was doing some research on Koi fish, I wanted to contact an expert before going through with my plans. Ok,

I am interested in purchasing:

2 Koi

2 Butterfly Koi

and a nice mixed selection of goldfish (about 3-4 each)

Calico Shunbunkins, Comets, Rynkins, Moors,Veiltails and Red/Calico Fantails

Here's the thing:

I live in NYC, so I dont have a pond, I am willing to purchase whatever size aquarium, even if I have to get a custom made aquarium. I REALLY want these fish, I absolutely love them. I would prefer if I can place them in one tank, but if you suggest me seperating the Koi in one aquarium I will do so. Please give me your opinion about my idea, what do you think I should do and all the information you can provide.

P.s. Within the next month, I'm moving into a Loft, with more than enough space, If it is possible to have them in one aqaurium, what size gallon aquarium would you recommend for these fish?

Even though I want alot of fish, I don't want you to recommend a  aquarium that gives them JUST ENOUGH room, I want them to have extra room so they can be comfortable, so feel free to add on more gallons if you feel its the best thing for the fish.

Also if this is an idea that you think will work and be healthy for my fish, how often would you recommend cleaning? Please all the advice that you can provide is truly appreciated.

Thank you so much in advance,

Celena


Answer
Hi Celena,
Wow! That's going to be a large aquarium. It will be gorgeous but really big. A koi aquarium is going to have to be at least 1000 gallon. Reason for this is that that they will get to be at least 3ft. long and also they are going to produce a tremendous amount of waste. The only information I have ever read has been to start with at least 1000 gallons and that is usually in the form of an outdoor pond or sometimes I have seen indoor ponds that look really beautiful.  Remember too that water is very heavy and the larger the aquarium the weight of the water is going to be tremendous. Also, if it is a glass aquarium the weight of the glass is alot since it will be very thick. Make sure your foundation can support it. Also, filtration must be excellent. It would be best to over filter any Koi or Goldfish since they both produce so much waste. More than tropical fish. You would also need to clean at least weekly and remove 30-50% of the water just to be sure it stays healthy for them.You would also want to buy a water test kit so you could make sure the water conditions remain safe at all times.
As for the goldfish, they need to be kept in at least 10 gallons per fish. I have a 29 gallon tank with only 2 and I have to do a 50% water change twice a week just to be sure their water is clean. You would have to decide exactly how may goldfish you want to keep and then do the math on the amount of gallons you would need. It will be a beautiful aquarium. Just be sure to not over crowd and keep it very clean.
It would probably be alot easier to keep the Koi and Goldfish in a separate aquarium since it would really have to be huge. It would be easier to clean too since a really huge aquarium takes a lot of work to clean and refill unless you intend to have it maintained by an aquarium maintenance service.
If you decide to still keep the Koi and are not going to create an indoor pond then you will have to have an aquarium that allows them enough surface space and enough room to turn around when they reach several feet long. Some people raise Koi from a very small size until they get fairly large and can no longer be kept in their aquarium and then they return them to a fish store and replace them with new younger fish. That way they can always have Koi but they never get too large for their aquarium and they don't have to buy a huge tank. I don't know how you feel about doing that since sometimes you can become attached to fish and don't want to give them up but if you think that is not a problem you might want to try only keeping them until they get larger and then returning them to a fish store and buying smaller ones. You wouldn't have to buy a very large tank and could possibly keep both the Koi and Goldfish together depending on how many fish you decide to keep of Koi and Goldfish. It would still have to be a large tank but not like a public aquarium! You could probably buy a 200-300 gallon aquarium and overfilter it with either a very large cannister filter or even possibly 2 might be better. Make sure you keep a schedule of frequent large water changes and not over feed. They will act as if they are starving all the time but you should only feed them maybe twice a day. They will eat until they make themselves sick.
Just remember with either of these fish and aquarium size--the bigger the better. Don't put too many fish in at once and you absolutely must cycle the tank or tanks before adding the fish. If you don't the ammonia will kill the fish quickly. Since an uncycled tank will have a lot of ammonia and nitrites at first, if you were to add the fish, and since they are known to produce alot of ammonia and waste, you would have a disaster. So please be patient and cycle the tank and gradually add a few fish at a time. Each time you add more bio load, by adding fish, it takes your tank time for the bacteria to be able to handle it. I see this happen so much with people buying an aquarium, filling it and immediately adding fish and then have them all get sick. Just be patient and it will work out very well and you won't have problems.
I hope I have helped in some way. Just be careful with adding the Koi since they do get really large unless you can provide a huge area for them. I know an indoor pond might not be practical but I have seen some really cool ones that have been made or you might even have someone install one if you have the room. Sometimes, Koi owners that have outdoor ponds contruct indoor ponds to house their Koi during the colder winter months. All they really do is contruct an outer wall out of board or cement blocks and a rubber pond liner is installed and the walls support the liner. A filter is added and that's about it. I have seen one indoor Koi pond that was done with the boards and it wasn't really very deep and was about an 8ft. square area. The Koi are beautiful and huge! It has a few large plants also which really makes it look great. A very relaxing mood for a room. Koi in ponds become real pets and love to be hand fed too.
Best of luck in your new adventure!
Hope this helps,
Karen