Maintaining your aquarium at the right temperature and pH balance, and including one of the different types of "algae eater" fish, will help to keep algae growth from getting out of control. But no matter what you do, there will still come a time that you need to clean the tank with your own two hands. That can be pretty nerve-wracking if you've finally gotten a good balance going in your tank's ecosystem; we're all afraid to do something that will hurt our fish when we start cleaning. Most important tip? Soap, of any kind, is lethal to fish, even in small doses. Don't use soap in your tank, or on your buckets or tools! I have bought a new bucket for each tank I've set up, and labeled it "AQUARIUM" with big red letters so that it doesn't get used for anything else.
Start by cleaning the inside of the glass on your tank using an algae scraper or pad labeled for aquarium use (the ones you get at the grocery store often have soap or other chemicals on them). You can use a razor blade to scrape any really stubborn residue off of glass (use a plastic tool to scrape an acrylic tank). Next, you can take out and clean any decorations, like rocks or plants, which are visibly dirty.
Just scrub them with your algae pad and rinse them under tap water. If anything needs deeper cleaning, I soak them for no more than fifteen minutes in a 10% solution of bleach (1 part household bleach to 9 parts water), scrub, rinse, and air dry them to let any remaining bleach evaporate. Now that all the gunk you've removed from the glass and the plants has settled onto the gravel, you can use a siphon to suck out the debris - there are lots of different siphons available.
Then clean the light, the cover, and the outside glass with an aquarium-safe cleaner. Trust me, you do NOT want to use regular household glass or lime cleaners - buy your chemicals at the fish store and rinse very thoroughly! Important Tip: By cleaning all the visible algae from the tank, you've greatly reduced the number of bacteria available to sustain the nitrogen cycle. I'd recommend that you do NOT clean the filter at the same time, because it harbors enough bacteria to get a healthy cycle started in your tank again.
I always wait two to three weeks after an aquarium cleaning before cleaning the filter. If your filter uses absorption (carbon, ammonia absorbers, ion-exchange resins), you should just replace it. If it's a mechanical filter (ceramic rings, filter fiber, or sponges) you can just rinse it gently in water the same temperature as your tank, and quickly put it back in place - that way you won't be killing all of the bacteria.
Finally, don't forget to clean out all the filter tubing and other nooks and crannies with a filter brush, to keep the filter working well.
Together with Iszuddin Ismail, Mic Hudson is sharing his wealth of knowledge on saltwater and freshwater tropical fish tanks. You can start with a free ebook on decorating your fish tanks. Download Fish Tank Aquascape at http://www.PetFishGuide.info