The best water for aquariums is well water: it’s clean, clear, odorless, and free from decaying substances. You can also use water from pristine streams or springs, provided it doesn’t carry unpleasant smells or tastes from mineral salts or other impurities. The same criteria apply to well water.
If your aquarium houses only one species of local fish, it’s often best to use the water they were previously living in, if possible. Clean rainwater can also be used for the aquarium, provided it was collected directly in clean containers and not as runoff from dirty or painted roofs.
In cities where tap water is the easiest option, it’s best to let the water sit in a clean open container for at least 24 hours so chlorine can evaporate before you use it to fill the aquarium.
Here are some additional tips related to specific situations and phenomena in the lives of fish and plants in the aquarium.
Foam on the surface of the aquarium indicates that the water is low in oxygen, especially when fish rise to the surface and gulp for air. Foam can also appear after fish overeat. In both cases, add a few cups of cold, fresh water to the aquarium or increase aeration.
If you notice a mucous-like film on the water’s surface, dead animals or uneaten food are probably decaying in the aquarium. When these clouds or films appear, drain and replace all the water, rinse the plants, and replace the substrate; otherwise the fish may die from the decaying water. Before doing a full cleaning, try skimming the film off the surface and add a little salt or saltwater. If the film returns, proceed with the complete cleaning and disinfection.
A grayish film on the water resembles the previous one but is harmless. Collect this film by gently submerging a cup into the water; the film will flow into the cup along with the water. It’s even easier to use a bottle: submerge it so the opening is almost touching the water’s surface and the film will be drawn in by the inflowing water.
A whitish film on plants, resembling mold that sometimes covers bread or cheese, is a colony of harmless microscopic organisms known as “infusoria,” which can be gently wiped away with a piece of cotton.
Sometimes tiny, thread-thin worms appear on the bottom of the aquarium. These worms are harmless and make good food for fish.
Cracks in aquarium glass are most often caused by improper placement, such as tilting or bending the frame. Place the aquarium on a flat, level surface to prevent cracking. If the glass does crack, seal it immediately with wax. If water starts leaking from the crack, drain all the water, align the glass pieces together, and seal the crack with hot wax.
Cracks in aquarium walls can also be sealed with a special putty. The best putty for setting glass in an aquarium is a mixture of Portland cement and oil varnish. Pour some cement into a metal or clay container, add a bit of oil varnish, and mix until a thick paste forms. Before inserting the glass, coat the grooves with this mixture. Allow the putty to dry thoroughly for three days before filling the aquarium with water.
