Algae grows naturally in aquariums. In small doses, it is beneficial to fish. But it can coat the inside of the glass and grow on every object, large and small, quickly creating an unsightly and embarrassing centerpiece.
What's a fish keeper to do?
Watch where you place your tank. Do not place it near windows or in direct sunlight. The more light the tank gets, the greater the chances of algae growing out of control.
Monitor the hours you keep the tank lights on. Try for no more than 8 hours a day. If you enjoy the lights on the aquarium (and who doesn't) take stock of when you are actually around to enjoy it. I have mine on for about three hours in the morning and about five hours in the evening.
Wash off the algae. I have two sets of decorations. When one set gets more algae than I'd prefer to have (and my tolerance for algae is pretty low) I remove those and put in the second set. And how do I clean the algae off the first set? It's easy. The best cleaner for fish tanks is: baking soda. Yep, that's right. I rinse off the decoration, then I place it in a shallow pan and sprinkle baking soda all over it. You can rinse it off after a few hours or a few days, depending on the severity of the problem. If you fail to rinse all of it off, it will not harm the fish - but it will drop the Ph. So you'll want to rinse it as thoroughly as you can. Using a toothbrush that you never used before is helpful for brushing off any excess algae.
Stay away from fast-acting algae removal products. They work by eliminating the elements in the water that algae feeds on. But it can zap so much of the minerals needed for the fish to live that they will actually suffocate. I watched an entire tank suffer due to one of these products and it is heart-wrenching.
Clean the glass yourself. I've used a number of products to clean the inside glass and the best I've found is a simple sponge (AKA algae pad) on a long handle.
There are also magnetic sponges sold that are very helpful when your fish don't like your hands in their water - like the parents of the baby fish they are protecting.
Hire someone to clean your glass. I like plecos. Because my angelfish get so large, I prefer to have one pleco in each tank. They can grow to five inches long (the bushynose pleco) to more than 21 inches in length so check with your pet store to find out how large your pleco will get when it is fully mature. They love algae and will spend most of the night time hours scouring your tank for it.
Do not get ottos for an angelfish tank. They are excellent at cleaning algae and I use them in my guppy and neon tetra tanks because they are a similar size. But they are so small that angelfish think of them as food. And since ottos can be very bony, they can injure the mouths of the angels who taste them.