Dabbling

It depends on the types of fish and substrates you have. Never overcrowd your tank. You can manage with a 10% water change every week and a tank clean once every 2 months. You can extend that 2 month period with live plants and good gravels that absorb dirt and 1-2 catfishes.

Feed your fishes only as much as they can consume. Stand by, feed, watch them finish, then feed again if needed. Food is the main source of dirt for the tank. Keep the food lid tight.

Do not have direct sunlight on your tank unless the species demands it. Think extremely careful before you introduce something into tank, be it a fish or food or plant or decoration or even water or light. Everything affects the composition of the tank. Most beginners make this mistake. When you want to put in a fish, don't pour the water in. Pour it out and just filter the fish and introduce only the fish into tank. As long as you introduce the very minimum into your tank, and have a watch on what goes in and when, you shouldn't have a problem with disease or algae or unclean water. If you're planning to make water changes, tap the water overnight and treat for chlorine, etc. Never hose it directly from the tap.

How do you heat a Small Aquarium without a heater? I've just moved from a tropical climate to a cold climate. I had some tropical fish back home. I got some swordtails today. The weather here has changed drastically. How do you heat a tank without a heater?

Until you can buy a heater, you can heat your tank using light. You can put 3 or 4 60 Watt light bulbs over a 10 gallon tank to heat it in emergency situations. Trouble is that when you turn the lights out to go to bed, the aquarium will cool off. The heating/cooling action can cause a great deal of disease and stress in fish just like the rapid changes of weather that you are describing. It would be best that you purchase a proper heater.