There have been many people asking, "how small of a tank can I use for an Anemone?"
This is my opinion- 20 gallon.
Below is one of 3 that I used to have set up.
It had a Coralife fixture on top with 2-96 watt bulbs in it. I still have these fixtures
and they are now for sale. I also have new bulbs for them still in package from Foster and Smith.
Not a good picture but back then the digital camera's where not like they are now.
2. The reasons The reasons for this are....... More water volume and more space for it to expand. With smaller then a 20 gallon tank you don't have the opportunity to add two Power Heads to the tank to keep the water moving. Filtration is hard in a smaller tank because of what you have to feed the Anemone. Silversides are large and will foul the water fast if it is not eaten and the waste from the Anemone also adds to the problem.
Keeping a 20 is much easier to keep stable as opposed to a 10 gallon tank.
3. Reason 2
The next reason is lighting. It is much easier to purchase a VHO fixture for a 20 gallon then a 10. Also, your tank needs a Skimmer. A 10 gallon tank is impossible to find a Skimmer for. But there are many that can be purchased to fit a 20 gallon tank.
I kept CoraLife fixtures over my smaller tanks and they are on legs made for them. They have 96w bulbs and I like the duel bulbs(half Actinic and half Sunlight) . They make for great color in the tank.
The more light wattage the better for them. However, I have to add, I have never nor intend to use Metal Halides for any of my tanks I see no need as I have no hard corals. A normal screw in bulb with a cheap fixture that comes with 10 gallon tanks are not near the amount of light you will need to keep an Anemone happy and healthy.
4. Filtration in a larger tank
I have hang on filters on all of my tanks. I prefer the AquaClear filters and use the 500's on all of my tanks. They move the water fast and take a lot of filter media and Charcoal. Very easy to change out the filter pads also. My opinion is they are the best on the market for filtration.
I hate the canister filters, way to much work keeping them clean and also are a pain to disconnect from the tank to clean. And they are Nitrate factory's if not cleaned regularly. I have also found that they do not move as much water as the hang on Aquaclear's
Adding an Aquaclear to a 10 gallon is possible but it would have to be a small one and that will not move the water or filter near as well as a bigger unit. Here is a picture of one in the box.
I was able to purchase 3 of these at a great price from a person on Ebay. I love them. (Remember to cover the intake!) See the section on that subject
I absolutely insist on at least 2 Power Heads in my tanks. One in each back corner if the tank is over 20 gallons. I want that water moving in two directions and coming together in the middle of the tank pointing straight forward to keep the water moving around at all times. I will add a third one if I can fit it in and add it to the middle pointing down to keep some water movement on the sand. But not to much as to keep it from blowing around. I really like the "Hydor Koralia" Power Heads because they can take
(sold separately)large Magnets to attach them where ever you want in the tank. You can see them on the "125 gallon tank".
They come in several different sizes also and can be bought on line for less then SW stores sell them. So remember, That cute little silver dollar size Anemone will grow fast when fed properly so why not get him a good size home with the needed lighting and filtration right from the start to take proper care of him.
I had placed a really tiny clone in a 10 gallon tank, within 3 weeks it had outgrown it. Stung everything around it and was up to the top of the tank with some of its tentacles out of the water. That was not good so he was moved to a 45 gallon tank immediately.
Here is the little fellow I am referring to in the 10 gallon octagon. This was back in 2004. She was taken from this dead coral and added to the tank. (I no longer have this tank set up.)
Another problem is skimming the tank which is a must for small tanks. I have yet to find a skimmer that will fit outside of a 10g tank . I have purchased several that go inside, they work OK but sure take up a lot of room and are ugly.
I have one in the 10 gallon above, It is on the on the left in the picture. I hate the skimmer. It takes up at least 4" of space in the tank. (I have 2 for sale) Just another reason for a larger tank.
So please consider purchasing at least a 20 gallon tank if you are just getting started. Best of luck