I think 50-55 gal will be a nice sized tank for your 5 goldfish
Includes: Aquarium Used For: Freshwater Fish & Saltwater Fish Tank Size: 55 gallon
Personally, when stocking average tropical community fish I’ve always thought about twenty to twenty-five fish were plenty for a tank this size. On the other hand, I’ve also had as few as seven in a 55-gallon tank. Really, it depends on the size of the fish, how much space they require and where they will occupy that space in your tank.
However, buying a large tank is not feasible either as you have to spend maintenance costs equally as the purchasing cost, and it’s not a one-time thing. The expenses can become a drag and eventually will turn into an inevitable hole in your pocket. So, if you’re looking for a fish tank and are buying it for the first time; the best-suited size is 55 gallons. Therefore, choose the one that suits your budget, requirements and environment and buy one as soon as you can and magnify your interior’s beauty.
Aquarium Dimensions and Weights - The Spruce
Jan 3, 2017 - A chart with standard aquarium sizes and filled weights
Anyway, I was looking at making a sump out of a fish tank but I wasn't sure what sized tank I should use for a 55 gallon main tank? What size should I use? I was going to have a protein skimmer and refugium in it.If you already have a 55 gal tank, then fine, it will probably work for your oscar by himself. However, if you are buying a tank from scratch, I strongly recommend that you get a 75 gallon (286 liter, 4 feet by 18 inches, by 20 inches) or larger tank. This is for two reasons. First of all, a tank with a single fish in it is somewhat boring to most people. At some point, you will probably be tempted to get more fish. With a 75 gal (or larger) tank, this is a possibility. The second reason is because it is quite possible that you will end up with a larger than average oscar. Oscars can and do grow up to about 18 inches (45 cm). A 55 gallon tank is simply not big enough to house a fish of this size. If you have a 55 gal, and you end up with a monster like this, you will end up needing to buy another larger tank. It is cheaper and more eficient to just buy the bigger tank in advance. When you consider the total cost of a complete set-up, the increase in price of a 75 gal over a 55 gal is not that big of a deal.The size of a 55 gallon fish tank depends again on the style of tank you select. The measurements of a rectangular tank will be much different from a tall, long or hexagon fish tank.- Choosing 55 gallon fish tanks can be a great compromise between small and very large fish tanks. Fifty-five gallon aquariums are beautiful and even more relaxing than the smaller sizes, but there are several steps to follow to ensure a safe environment in which your fish will thrive. These tanks are not small, so you will need a sizable space. Bob's staff will help you outfit your tank and give you advice on how to set it up.