When making an ecosphere, the first thing you should think about is the jar. It is the most important part of your ecosphere because it contains all the various organisms in your system. I don’t recommend using plastic containers as chemicals could leach into the water. They also tend to heat up quicker when in direct sunlight, which gives you less time to notice and move your ecosphere to a cooler place. For best results, I suggest using a minimum of 1.5L (approx 50.721 US fl oz) but any sized jar can be used with success. I personally preferer a 2L (approx 67.628 US fl oz) jar size because it allows for there to be a higher level of biodiversity in animals as well as plants without taking up too much space.
Jars that have a clip and rubber seal are best as they can be commonly found in the correct sizes and have a really good seal. Another great type of jar is the demijohn jar. They can have much larger capacities and have a great seal. The only drawback is that they have smaller entrances, meaning it may be harder to put plants or rocks in. Don’t let that discourage you though because in my opinion they are worth the effort and always look awesome.
If using a pre-used jar, it’s important to get it as clean as possible to prevent chemicals from previous uses from affecting the ecosphere. Regular dish soap is fine but be sure to rinse thoroughly. It is also good to dry the jars with a paper towel as tap water can contain chloramine which doesn’t evaporate unlike chlorine and could negatively affect your ecosphere (I have however never seen or had this be a problem for me so take this with a huge grain of salt).