The tank would be 20 gallons, properly airated, and would have a filter suited for 20 gallon tanks. 2 FantailsIf I were to keep 2 Fantail Goldfish in a 20 gallon tank, how often would I need to change the water?I would go with a filter for at least double twenty gallons. Look into Marineland Bio Wheel filters. Either the 150B or the 200B model would work. http://www.petsmart.com/product/index.js
No matter what, always perform your weekly partial water changes of about 25%. Do these water changes using a gravel siphon so that you may vacuum the gravel while changing the water. A lot of debris will settle on the bottom of the tank, and it needs to be removed.
With two goldfish in a twenty, I think it would be a good idea to test for ammonia in your tank daily. If ammonia is present, than perform daily water changes of about 10% until levels are at zero.
Be very careful not to overfeed your fish, and remember to remove any uneaten food from the tank within a few minutes of feeding.If I were to keep 2 Fantail Goldfish in a 20 gallon tank, how often would I need to change the water?Twice a week minimum of once a week also you need your tank over-filtered so you need a filter appropriate for 30-50 gallonsIf I were to keep 2 Fantail Goldfish in a 20 gallon tank, how often would I need to change the water?20% water change once a week for the fish u have u need a good filter because the tank will get dirtyIf I were to keep 2 Fantail Goldfish in a 20 gallon tank, how often would I need to change the water?If you have a good filter you never have to change water! You will need to clean the gravel with a tank vacuum to get the dirt out. But you never change the water in you tank once it is set up. I would go up to a filter for a 30 -40 gal tank.If I were to keep 2 Fantail Goldfish in a 20 gallon tank, how often would I need to change the water?Yup, twice a week preferably, once a week absolute minimum.
With a 20 gallon and two of these guy I'd at least double the filtration. I recommend probably 2 20 gallon filters, this way you don't have a huge water flow problem. Too high of a filter may be stressful on the bulky and slow moving fan tail goldfish. 2 20, or maybe 2 30gallons, gives you good filtration on both sides of the tank.
I'd also consider an ammonia reader that gives a constant reading, so you can have an accurate all day reading of the water quality.
Perhaps look into some live plants as well, to help control the nitrates in the water.
Best of Luck!
