Hi,
Welcome to Simply! I'm from CT as well Where in CT are you?
Yes you need to do water changes because you have fish in the tank. Do a 50% water change and be sure to get the entire gravel bottom. The water should not be cloudy Do not overfeed the Silver Dollars, that's why your water is cloudy. When you vacuum the gravel you will see how much food is wasted. If your going to get the 45 gallon, why not get the sponge filter and place it in this tank now? This way it will be cycled when you set up the 45 gallon. You can also do this with the aquaclear as well. That's what I did When you get the 45 all you have to do is add the water.
Frank