When it comes to choosing the right tank size for your five silver dollars, there are a few things you should consider. First and foremost, silver dollars require plenty of space to swim and explore, so ideally a 15-20 gallon tank is recommended. While this may seem like an excessive amount of water for just five fish, these larger tanks provide ample room for them to move around and grow into their adult sizes. Additionally, having more water in the aquarium also helps minimize fluctuations in temperature and pH levels which can be deadly for your fish if they're too extreme or sudden. Finally, larger tanks tend to be easier on filtration systems since they process less waste per gallon than smaller ones do; meaning fewer filter changes! All said and done, when it comes down to deciding on what size tank for five silver dollars is best – 15-20 gallons is most likely going to give your aquatic pets the optimal living environment where they can thrive.