They get huge. I think about 3 feet long.

If you don't have a REALLY big tank then it is probably best not to keep them.

How big of an indoor pond will you be building?? Clown knives can get up to 4 foot long! The filter system will also need to be heroic too to handle all the waste from those two big boys. I know people who come into the store I work at who have 3 footers and are using large tanks and animal watering troughs to house their big boys, I'm talking 200 gallons and up. With two Knives , 200 galllons will be a minimum for you. Enjoy your big boys!!

The indoor pond is going to be 480 (8x4x2deep). Thing of it is I have two marbled gobies (~20") and three bichirs (~12"). They're only about 4" right now because I was planning on a big tank for them but knew I had babies= *some* time. The tank *was* going to be three tanks but I don't think I can do that now (300 for the predators 90 for my community and 90 brackish). I was going to get the clowns *after* my tank was done but the guy was going to toss them and called me to come get them immediately. Now that I've thought about it I think I should just have the full 480 instead of 300...

Adrea

Cool, I wish I could set up a indoor pond, I'd like to have a bichir, polys are so cool. I'd do the 480 if possible. Have you seen http://www.monsterfishkeepers.com/
its a cool site for the lover of tank buster, bichers, knives, Gars etc, I think you'll like it, lots of good info on dealing with the big boys.

Thanks for the link maybe they can help me figure out how I'm going to have to shuffle the fish and divide the tank ;) I keep hitting a wall with the marbled gobies. The people that keep them normally go brackish for them but I don't think it's necesary by what fish base says about them. I know they're not keeping brackish ponds in malasia where they raise them for food either ;)

Adrea

I've heard about the brackish water for the marble gobies too and seen them on the wholesale sheets as both brackish and non brackish water fish. I've also heard of them doing well in hard water with no salt addded. Maybe they are not so demanding of the salt as much as the hard water conditions that go with brackish water.

I talk to a guy who had them before I think he's somewhere on the east coast and he had his for five years before he gave them away....no salt there.

My pH of 8 and kh of the same should work ;)

Adrea

You will need to cover the pond, knives jump and you don´t want to come home just to find your fish on the floor.

i had 2 for years in a 200 gallon i hope you have a good supply of feeder fish

The gobies like to jump if you change their tank too much too. I was so used to dealing with koi that I lost my first marbled over it. Water quality aside koi only jump out if you move them to a smaller container lol.

I plan on breaking the knives off of feeders actually. I have a bunch of livebearers but it's not enough to feed them more than once a month so far. I can get reasonable feeder danios until I get them on other foods. That was one of my reservations with these two. They've only ever been fed feeders but someone told me if I use garlic flavor I should be able to get them to associate the smell with food then offer other things.

Adrea

Teach them how to feed on pelletized food, toss in a feeder at a time, then drop a couple of food sticks ( Doromin ) and wait, if they don´t eat them immediately remove them and keep on doing it, eventually they begin eating prepared food.

I have a clown knife. He was 3 inches when I got him. I've had him for a year and he's now 12 inches. I have him in a 10 gallon tank which is awful so I'm trying to find a home for him. Just be sure not to put them with anything small enough to fit in their mouths. My clown eats goldfish. He won't eat anything that's not moving. They are beautiful fish for sure.

An Arrowana would be great for that type of setup[although there jumpers too].