It starts out slowly. The first day you get your fish, your tank is sparkling clean. A few weeks later you notice the tank is looking a little cloudy. You ignore it. Two more weeks go by and your fish tank is starting to look like mine did. This can be very overwhelming for a new fish owner. Don't sweat it, I've got you covered. Just follow this step-by-step instructable, and before your fish know what's happened they'll have a fresh, clean tank.

Step 1: Background

Before beginning the tank cleaning process it's important to note a few things first. This instructable is designed for small to medium sized tanks (5-20 gallons). The instructable is also designed for freshwater tropical fish, meaning that the water temperature is meant to stay in the mid 70's. The tank that I am demonstrating on is a rare case. It is much dirtier than it should ever be. Most cleanings should not wait until the tank is this dirty. In fact, every other week you should plan on cleaning your tank.

Step 2: Materials

Aquarium salt.
Water conditioner.
Fish net.
Temporary fish tank.
Water siphon.
Clean container.
Large bucket for waste water.

Step 3: Unplug Electrical Devices

The first thing you will need to do is unplug all devices such as the aerator, filter, and heater. I suggest leaving the hood lights plugged in and simply setting the hood behind the tank to help illuminate the tank.

Step 4: Remove Decor & Fish

Begin removing all decorations and electrical devices from the tank. Be carefully not to harm the fish in doing so. Once the decor is removed, you can next remove the fish. Fill your temporary fish tank with some of the original fish tank water. It is important to use the current tank water when filling the temporary tank as this will provide less environmental stress on the fish. Gently transfer all fish from the current tank to the temporary tank using the fish net. Be careful not to allow the fish to jump from the temporary tank. I recommend having a lid cover the temporary tank.

Step 5: Vacuum the Gravel

Now, you can begin the actual cleaning process. Use the water siphon to remove the dirty water and also vacuum debris from the gravel. The easiest way to start a siphon is to fill the vacuum end with water and then move the siphon quickly up and down several times. Make sure you have a large enough container in place to catch the water as you siphon it out. It is important to vacuum through all the gravel with the water siphon to remove fish waste and leftover food. You shouldn't have any problems with the water siphon vacuuming up the gravel as it will be too heavy. Remember to remove no more than 75% of the water from the tank. This will ensure that you do not remove all the vital bacteria that your fish need to survive. In fact, a typical clean should only require you to remove between 25% and 50% of the original water.

Step 6: Clean the Glass & Decor

Wipe down the inside of the glass using either a clean rag or paper towel. Do not use any cleaning chemicals such as soap to help clean the glass, as this can harm your fish. If you own a plecostomus, I suggest leaving one of the sides of the glass untouched in order to preserve some algae for the pleco to feed on. You may also wipe down the outside of the fish tank if needed. Be sure to rinse off any decor items as well by simply running water over them.

Step 7: Refill the Tank

You are now ready to refill the tank. Begin by replacing all decor items including the heater and aerator. Do not plug these items back in yet. Grab your clean container and begin filling the tank with tap water. Try to refill the tank with water as close to the same temperature the tank initially had. You will want to fill the tank about 90% full to allow room for the aquarium salt, water conditioner, and fish. You may now plug in all electrical devices.

Step 8: Add Salt & Conditioner

Now that you have gotten all you water added and heater plugged back in, you are ready to add the aquarium salt and water conditioner. Read the instructions carefully for both chemicals, and add the recommended amounts of each into the tank. Allow the tank to sit for 15-20 minutes while the chemicals diffuse and the water temperature balances out.

Step 9: Return Fish and Enjoy!

You may now return your fish to their new and now clean home. I recommend cleaning your tank every other week. In doing so, a 25% to 50% water change should be fine. You should also change the filter every other week. Be sure to stagger the interval between your filter change and water change in order to preserve the helpful bacteria and to lessen the shock on your fish.

Step 10: Important Tips & Warnings

1. Make sure your new tank water is the same temperature as the water the fish are currently in. This will reduce the shock on the fish.
2. Avoid leaving your fish in the temporary tank for more than 30 minutes. Eventually they will run out of oxygen if left for too long without an aerator.
3. Avoid frequent large water changes. Typically you should only change between 25% and 50% of the water.
4. Never use any type of soap products to clean the tank. Soap has harmful chemicals that may kill your fish.
5. Never try to move a full fish tank. They are much heavier than they appear, and this will most likely end badly for you and your fish.