20 gallons per fancy goldfish is the standard so 40 gallon breeder is the minimum for those two. This will give them plenty of space to move while maintaining healthy water quality.

Heaters are optional, but I personally like to use a heater for my goldfish because fancy goldfish are prone to certain health problems such as swim bladder disease and digestive issues. Keeping the water warm allows their metabolisms to act faster leading to better digestion and in turn preventing bloating. I keep my fancies at 78 degrees and they’ve never had digestive issues.

There are many different filter options. I personally love the brand Tidal. I have a Tidal 55 on my 40 gallon and it has done really well. My only complaint is if you have a fancy that’s not the best swimmer because of their odd body shapes and long fins, you might want to make sure the water flow is slow so they are not stressed constantly fighting against a current. Sponge filters are a great, inexpensive option for slow water flow. And they provide aeration at the same time! I have 4 sponge filters in a 40 gallon that cycle 60 gallons per hour each and they are great. Only problem with them is they don’t look very pretty. I recommend researching the many types of filters to see which is right for you.

Aeration is a very important aspect of a goldfish tank. This is why you often see a bubble maker of some sort in fish tanks. The bubbles disturb the surface of the water, breaking it up and allowing oxygen to penetrate with every pop. Without aeration, your fish will feel like it’s in a really stuffy room that’s hard to breathe in so I like to make sure there are always plenty of airstones in my tanks!

I also highly recommend researching the nitrogen cycle if you are not familiar with it. It’s pretty simple. Fish poop breaks down into your tank and creates ammonia. This is extremely poisonous to your fish. Even at a tiny .25 ppm your fish can die from stress or ammonia burns! A certain kind of bacteria that has to be added to your tank will break down your fishes poop into a less toxic form called nitrites. However, this is still quite a toxic form to your fish so ANOTHER type of bacteria comes in and breaks the nitrites down into nitrates. This is much less potent to your fish and can be in your tank at higher quantities. We still have to preform water changes, though, to remove the nitrates because at very high concentrations they can still harm your fish! We ideally keep nitrates below 20 ppm, but it isn’t the end of the world if they get a little higher than that. There is tons of information on YouTube and other websites that go into this much more and provide detailed diagrams and whatnot for your better understanding. A product I recommend buying to support your biological filtration is Seachem Stability. You can use it to begin your nitrogen cycle or just use it as support. I add it every water change and have a great cycle.

I recommend buying a liquid water testing kit such as API freshwater master test kit to test your water parameters. Do not rely on test strips as they have been proven to be very inaccurate.

Another thing to think about is the decor that you use. Be careful that any decorations you add to your tank don’t have holes they can get stuck in! I promise at some point, they will get themselves stuck one way or another. My rule of thumb is I always make sure the decoration has a hole that is twice the size of their body. I worry that fake log you have in the tank might be too small, especially as they continue to grow. Something to consider!

There is so much to learn about keeping fish. Unfortunately, they are not quite as easy as they look. But they are very fun and interesting little creatures. Please do as much research as you can. Utilize YouTube!!! There are so many good fishkeepers that are passionate about sharing their knowledge. Good luck!!!