A few years ago, I purchased a new 6 sided tank for my large goldfish that I'd raised for years and years (Orandas and Ryukins) This tank is 20" wide in circumferance and 2' deep. When we moved our fish from their rectangular tank to this tank, they never really seemed "happy." Previously very active, they spent most of their time floating in the middle of the tank and not swimming much. Eventually they died off, one by one after many months, much to my horror! The tank had been cycled correctly, and the water was properly monitored. The HOB filter was actually for a bigger tank measurement, but we thought it would provide the extra cleaning goldfish need.

I would like to set this tank up again, and again raise some little goldfish into BIG goldfish, as I adore them. This tank has been sitting empty for years in my storage, but I want to ensure I do this right. If their death has anything to do with tank shape, putting more goldfish into it again would be terrible.

Could the shape of the tank have had anything to do with it? (The only "variable" factor is that my hubby took over their care and he fussed with them too much, IMO. I don't know if that, and/or this tank contributed to their deaths.) Does tank shape have anything to do with fish type selection??????? Does it matter if your tank is rectangular, or cubed?

Could it have been the filtration system and how it works in a deeper tank have had something to do with their demise?

I've heard a few things about goldfish since I brought this specific topic up, and I'd like to know if this is true? Any advice would be greatly appreciated!

Goldfish like long tanks as it suits their swimming style so an upright, cube style tank isn't good for them. True/false? Goldfish likes lots of surface area and this tank doesn't have enough only being 20" across. True/False? Fish find multisided tanks stressful so I should cover 3 of the 6 sides with a background? And last but not least, I should increase my filtration system from just having a HOB to include a canister as well to help with filtration.

I am not schooled in keeping fish, but I can try and help answer several of your questions.

1) I feel that all tanks need both a bottom and a top filter, and this is even more true in my eyes for a taller tank such as yours. You could supplement the hob ( hang on back ) filter with a sponge filter at the bottom or a cannister filter with the intake at the bottom. You are really limited on your HOB options because of the size of your tanks.

2) I think that gold fish love to swim side to side more than up and down. My personal opinion is that the tank is not optimal for large goldfish. You can walk up stairs, but do you really want to? I'd much rather walk on a level plane than up hill.

3) I would agree, cover some sides of your tank with a background. I don't know if there is science behind this or not, but my fish like it better when they feel secure from some sides.

I will not say that this tank is not good for your fish, I am just giving my personal opinion on the tank and your questions. Feel free to interpret them as you will.

Best of luck!

From your description, I am guessing you have a hexagon tank if it's 6 sided. Although you could put goldfish in a tank like this, the best type of tank for a goldfish would provide more lateral swimming space and is not too deep. the tank that you have would actually be good for angelfish who do not require too much lateral swimming space and are good with vertically tall tanks.


with a deeper tank, it's difficult to get the water properly aerated near the bottom. goldfish being huge poopers create lots of waste and need really good filtration and aeration in their tanks. that and swimming space are what make your hexagon tank far from ideal.

of course if this is your ONLY option, it would mean you'd need to keep really close watch of your water parameters to make sure the water quality is tip top shape.




~ yes goldfish would prefer a long tank rather than a tall...
~ more surface area means more air to water exchange at the surface and better aeration
~ i think with the sides being covered, it depends on whether or not there are many "startling" types of actions going on... if there are going to be little kids darting around the tank or lots of scary movements, covering the sides might be a good idea. if it's against a corner of a room, then i think it would be ok.

I have heard that the surface area of the tank is a big factor in how much oxygen is being allowed to the fish. So a long rectangular tank lets in more oxygen to the fish than a tank that is deep but has a small surface area. Your fish may have went from a tank that allowed a good amount of oxygen to one that was poorer. You could try putting a type of filtration on the bottom and top, and putting some sort of aeration at the bottom of the tank along with a bio wheel filter which lets a lot of oxygen in.