We are hoping to upgrade our current tank for a larger one sometime over the next few months. This new tank we want to be big enough to last our fish for the rest of their lives. We have four Fancy Goldfish (two Black Moors, a Ranchu, and a Pearlscale).

We are unsure whether we need to go for a five foot tank with dimensions of either 60" x 24" x 24" (149 US gallons) or 60" x 24"(H) x 18" (D) (112 US gallons) or a four foot one with dimensions of 48" x 24" x 24" (119 US gallons) or 48" x 24"(H) x 18"(D) (90 US gallons)?

Do they need the length of the five foot or is the actual volume of the water more important - the 48x24x24 having more volume than the 60x24x18 - or would a four foot one with a large volume be sufficient?

Hello Karly, i personally would opt for the five foot tank. goldfish tanks should be longer rather than deeper as this gives a greater surface area for oxygen. the five foot one you have mentioned is 124 uk gallons and would be more than ample. the smallest tank you mention is still 74 uk gallons which, if you use the rule 10 gallons per fish is still more than enough for 4 fancies. the bigger tank would help with water quality issues. but with good filtration and a good supply of air all of those tanks would be ok for 4 fish. once again, if it was me i would get the biggest tank that space and money would allow. hope this has helped.

I agree with alistair's points. Even by the "10 gallon rule" (which is 10 US gallons BTW), the smallest tank you mentioned at 90 US gallons would allow over 20 gallons per fish. A 90 gallon tank is quite a large one and I would say that would more than accomodate your 4 fancy goldfish for life, you could even increase the stocking if you chose to once it was established. Generally speaking, the larger the tank the more the "10 gallon rule" of volume is less important than the actual dimensions of the tank, such as the length, as well as the level of filtration you have in place. Although, allowing 10-20 gallons per fish, or even more is of course better. So, you do have more flexibility with stocking with larger tanks

I have to agree with Allistair and Bumble 100%. Having watched all my fish in different shaped tanks I am really convinced that length rather than depth is what they need and prefer. You could have the water level lower if the tank is longer and still have the same water volume. It is actually recommeneded here in Japan for fish with swim bladder issues to have lower water.

Ideally, I would like to get a five foot tank but, realistically, it is looking like we will have to get a four foot because of the financial cost and space needed for a five foot. We are still living in rented accommodation so we are facing at least two more moves before we are able to buy our own house.

If we end up with a four foot, then we are not going to get less than a 48 x 24 x 24 so we can, at least, get the volume.

Well in the end where you have space is a major consideration. Whatever upgrade you get is always better than not upgrading .

I agree, lack of space is often the most frustrating part of fishkeeping, partucularly lack of space in any particular place to locate a tank. I'd love a 4-5 foot tank too, but at the moment I have to make do with three seperate 3 footers