Nano tank good for beginner?

[fishfanatic]

How does the filter work on the biocube? Do you have to replace a sponge once a month? Do I need a power head or is the filter enough water movement?

 

[fishfanatic]

I feel so overwhelmed right now! I feel like I know nothing. Is salt water the same as fresh water? (Just add salt). I want SW more than anything but I don't want to get above my head in bills. I actually don't have any bills, I am 16 years old. I have a job and I make about 300$ a month I want to save at least 60% of it. So that leaves me with 135$ a month. To spend on fish. I already have a 40 gallon freshwater tank (40$ a month). Could I run this tank on less than 95$ a month? If I could spend less money that would be great.

 

[fishfanatic]

Do I need a power head?