I would look in the local classifieds for a tank. Fair value is a $1 a gallon used. I found one in my local paper 125gallon with filter and other equiptment for $150. If you are handy you can save alot of $$$ with DIY tank stands, Lighting(especialy is the tank is 48" long like 50,75 and 90 gals.)and even filtration. If you need some ideas for DIY let me know. I am planning an indoor pond/aquarium down the road. It will be in my basement when I get arround to finishing it. I was going to use all local natural rock for constructin with a pond liner but have side veiws with acrylic "windows". This link has some good ideas I have a lot of others that are also good or just do a search for DIY aquaria, Good Luck.

Here is a link that might be useful: DIY site

At only a foot in 5 years, it's clear that the current tank has kept your butterfly koi pretty small in comparison to pond koi. Definitely don't go smaller than a 100 gallon tank - larger if you can. Your comet will also benefit from the size of the tank.

DO keep in mind that koi also tend to love to leap up and out of water from time to time - so you want a good fitting lid as well.

Another consideration if you have a spot in your house that can take the weight load is to build an indoor pond setting. This is something I'm considering to do for my indoor fancy goldfish since I have a porch area that has a concrete floor. This way you can make new digs for your fish the size and shape you want.

IMHO a koi does not belong in any aquarium except perhaps for a short tuerm QT treatment. They just grow to large for such an environment and are a heavy load on any filter system typically found on most aquariums. I fyour bf koi is as small as it is its stunted for sure either by insufficient feeding or its environment. The koi in addition to a 9" goldie is just a bad setup. My GF grow from small feeders to well over 6" in length in less than a year in my pond, and my koi are all well over a foot long by 1 year of age. NOt trying to sound harsh, but koi and gf as such are not aquarium fishes. You can get by with some of the fancy ornamental GF breeds like a black moor or Ryunkin etc, but the red/white (usually a sarrasa) and koi are just not suitable. Build a pond and net it. Lots of folks like me live in the boonies with lots of natural predators and raise koi and gf just fine.......there is ways to deal with predators such as feral cats.

Thank you woeisme for some great advice, especially regarding fair pricing and the DIY links. Now, I feel better knowing I won't break my bank account.

I also appreciate your imput on the cover and the possibility of an indoor pond, Skygee. All my tanks have been covered since my first aquarium, over 15 years ago, when I had a suicidal Harlequin rasbora, who jumped out the tank 4 times and then lived 2 more years after the last jump! But the new tank will for sure be covered. My turkish Angora, Lily, would just love it if I put my koi in an indoor pond, but I don't think she'll get her wish.

Now, for clarification, I acknowledged in my initial post that I am well aware that the environment for my koi and goldfish is not ideal, so I would be grateful if the focus of future posts would not be on how bad my setup is, which no matter how well-worded, is still harsh and not, I believe, the point of the learning environment of a forum. Please focus instead on advice on how to upgrade to a 125+ gallon system.

Also, a pond, whether indoor or outdoor, is just not an option for me, so if this is your opinion, then just don't reply to my initial post. I know that there is debate on this issue, so I'd rather not cause trouble.

I appreciate everyone's imput so far, and I will carefully weigh all my options before I make my final decision.

Warmest regards,

lljdma06

I think a 125 gal would be suitable. 6' of side to side "should" be adequate. I never had Koi before so I am not to familiar with the breed. A good sump style filter is a good idea for larger tanks. You can make the sump as large as you want. It can be stored under the tank in a cabinet. The larger the sump the more water you actually have. Also media changes are simple as long as you design it right. The DIY link should have some examples. Another option is a filter like the "magnum" series by Marineland. They usually come with a micron cartridge as well as a every day cartridge. The micron filter is for "polising" the water. The addition of a few Tbsp. of D.E.powder before the micron cartridge will remove even more crud. You can polish as part of a weekly routine or as needed.

I recently began keeping Butterfly Koi in an aquarium. Would you be willing to share your experiences on AquariumâÂÂs Butterfly Koi at http://abfk.forumotion.com? it's a new forum I created for just Butterfly Koi owners who prefer raise them in aquariums than ponds.

There will be no judging or condemning fish keeping habits at AquariumâÂÂs Butterfly Koi. Keep in mind that it is a new forum. So if you are interested just register and start posting.

Here is a link that might be useful: Aquariumâs Butterfly Koi