Changing the aquarium water is probably the most laborious job for the home aquarist, but putting it off often leads to algae growth and sick fishes. It is impossible to say exactly how much and how often, but as a general rule the water should be changed at least two or three times a month. This is because tap water is rich in CO2 and it replaces vital trace elements. The replacement of these trace elements is essential to the growth and development of aquatic plants. Sometimes people complain that their fishes have died from frequent water changes. This is almost always the case where the water hadn't been changed in a long time, thus the fishes were affected by either pH shock (the old water must have become acidic) or a sudden drop in the amount of filter bacteria (especially if the filter was cleaned at the same time, always a bad idea), which led to sudden acidification. The trick is simply to change the water in smaller quantities, but much more often. One good method is to store a reservoir of water in a separate tank, let it stand for 24 hrs and aerate the water with an airstone before changing the old water in your aquarium. By using this method, the aeration will eliminate the harmful chlorine commonly found in tap water. Water changes can be done as frequently as daily for some setups.
Plants should be closely watched in hot summer weather, even though the dog days of summer may have us feeling lazy. Plants and fish are more sensitive to heat than we are, so even a small rise in temperature can have disastrous results for our planted tanks. The aquarium should be kept in a continually air-conditioned room near the A/C. Otherwise, an aquarium cooler is recommended. The ideal maximum temperature for most aquatic plants is around 82 degrees F, and they can withstand temperatures of up to 87 degrees F for short periods. Water is generally two degrees cooler than the room temperature, so the room temperature should be set at 84 F. Of course, the lighting has to be taken into account as well. A fan directed at the aquarium will lower the temperature a few degrees. Some aquarists float bags of ice in the aquarium as a temporary measure. However, this is not a very good idea as the temperature in your aquarium will constantly fluctuate, causing more harm than good.
A more troublesome but effective way to lower the temperature is to change 70-80% of the water. Chlorine is less soluble during summer when the water is warm, so even large water changes won't lead to chlorine poisoning. Frequent water changes will promote growth during the regularly stagnate summer months. The stunted growth syndrome during summer is natural but is often mistakenly handled by adding more fertilizer.
Aquatic plants are at their best in winter. There is little special treatment to worry about, but some form of heating is necessary unless there is continuous climate control. A simple heater and thermostat system is easily set up, but the heater should have a lower electrical capacity than the thermostat. For example, if the thermostat's capacity is 300W, the heater theoretically should have a limit of around 250W. Thermostats often break as a result of strain, using more electricity than their capacity, so there should be a safety factor.
Most heaters do not affect the bottom of the aquarium enough, and roots can be damaged. This is especially a problem with aquariums that are kept in cold areas so that the thermostat is always on. One way to prevent heat loss through the bottom is to place Styrofoam underneath and around the lower half of the sides of the aquarium. Bottom heaters plates, such as the types manufactured by ADA, is another option. Bottom heater plates have their advantages as they provide even heat distribution throughout the substrate. It is important that bottom heaters have their own thermostats to prevent overheating and frying the roots.
The chlorine content of cold water is high, so water changes should be less frequent in winter. When the water is heated in a boiler, tiny bubbles of chlorine are formed which can get caught in the gills of fishes and do them great harm. Water should be changed a little at a time and aerated with an air stone or by pouring it from bucket to bucket in order to dispel some of the chlorine gas.