The Puffer Forum

I currently have a 30 gal cube tank (18x20x21) that is home to a brown knife (Xenomystus nigri), and a few blood fin tetras. My wife has fallen in love with puffers and we want to add one to the tank. Right now she really likes f8's, but I'm concerned that f8 likes slightly brackish water but the knife doesn't tolerate salt at all.

So will the f8 tolerate the same water conditions as a Xenomystus nigri (neutral pH, no salt) or should I try and steer her towards something like a South American Puffer that likes fresher water? Any concerns with mixing these two species in this size tank? Before you say the knife is going to outgrow the tank.... he is 4 years old, 4.5 inches and hasn't grown any in the past 2 years, so I'm fairly sure he's not going to suffer explosive growth and outgrow the tank in 2 months.

Can you suggest any other topwater fish that get along with puffers? Someone I know suggested African Butterfly fish. It's a tall tank and I'd like to have fish that make use of the whole depth.

No more fish of any kind. The tank setup has stunted the knife, so clearly, its too small to add any more bioload. F8's can't be in fresh water in captivity, it shortens their 15 year plus lifespan to a max of a few years, and SAP like high speed swimming, so it's terrible tank shape for them.

I should have been a little more clear in my other post. All my fish (the knife, the tetras and a small algae eater) are currently in a standard 40 Gal tank, and it is no where close to being crowded or over stocked. The cube tank is a new tank that I am transfering the existing fish to. I measured it when I got home and it is actually 25" high, bringing total volume up close to 40 Gal, so it will be nearly the same volume as my old tank, just spaced differently.

If the knife was stunted, it wasn't because of bioload. It has lived in the standard 40 gal for it's whole life, shared with the other fish. I have also been using a magnum 350 with dual biowheels, and weekly partial water changes to keep mineral concentrations high. I've discussed the issue with people at several fish stores and they have no idea why it isn't growing; food, water params and tank size all seem to check out.

How do weekly water changes keep the mineral concentrations high & why would you want to keep them high?

Are you asking about a puffer for the 40g tank then?

I was told that as the knife grows it leeches needed minerals out of the water and if particular mineral concentrations in the water drop low enough, it will stunt growth. I was advised to perform a small weekly water change to ensure that the mineral concentrations stay up.

Anyway....the question:

I am getting rid of the origional 40 gal and transferring the current fish into the new 40(ish) gal cube tank. I'm looking for a puffer to add to this new tank with the existing fish.

I would have kept the other tank for puffers. They are nippers & the knife wouldn't do well with that.

Water changes remove minerals not the other way around. Knifefish like softer water with low mineral content--I don't know where you got the incorrect advise.

The cube would probably work well for a trio of F8's if you don't mind going brackish, and they are one of the more laid back puffers. If you don't mind going near marine or marine later, it would work for a GSP and perhaps a single clownfish later if you cared to go marine.

I bought this new tank because I don't have room for a long tank anymore. In my old apartment, the tank was in the spare bedroom where the only time I would see it was when I fed them or worked on the tank. I switched to this new tank so it could actually be out in the living room. So setting up the old 40 gal for puffers is out.

As for the knife. I live in Indiana, which is known for it's hard water... I'm wondering if the water was too hard for the knife and that's what stunted him. (not really a puffer question but) how can you go about making your tank soft and acidic without increasing the salinity (like normal ion exchange units do) ? Would laying down peat substrate do it or would I actually need start aging my own water?

If it weren't for my knife fish, I wouldn't mind going brackish. We actually decided on the cube tank not only for the way it fits in the room, but because the dimensions make it perfect for a small reef tank later on.

If your knifefish has been living in your tap water for this long, I'm sure he's adjusted to the hardness. Adding salt will just be adding more minerals to the tank & this is the opposite of soft water. There is a brown dark water tonic folks add to their discus tanks. I believe you can get it at most LFS. Some people also add peat to a bag into their filter.

I'd forget about puffers at this point.

Also, most cowfish species grow to ~18".