Temperature
Water temperature affects the amount of dissolved oxygen water can hold. Cool water holds more oxygen than warm water. Obviously, though, we can't just lower our aquarium's water temperature to increase its oxygen content. Tropical fishes require warm water. While many of them may tolerate a fairly wide range of temperatures, they thrive and reproduce in a narrower range. A little research on your part can add to your pets' health. Good aquarium publications, such as FAMA, usually give optimum temperatures for the critters they cover.

Winter may create no special problems if you keep only species native to your region. Even inside your home, though, tropicals will need some added warmth.

Inexpensive aquarium heaters have worked well for me. More costly models have features and look high tech, but I'm happy with economical performance. No matter what they cost, however, heaters need to be matched to the size of the aquarium. In some cases, more than one heater may be needed.

An accurate thermometer is a must. Even heaters with thermostats marked in degrees need to be monitored with a thermometer; otherwise, you risk either chilling or cooking your pets. A good temperature range for many aquarium fishes and invertebrates is 72 degrees fahrenheit to 80 degrees fahrenheit. It's still best to check the literature for the optimum temperatures for the species you are keeping.

pH
As with temperature, aquarium fishes tolerate a rather wide range of pH; however, most of them prefer a much narrower range.

The pH of your aquarium measures the hydrogen ion concentration in the water. A pH of 7.0 signals a neutral concentration. A higher number signifies a basic, or alkaline, pH. A lower number indicates acidity.

Under normal conditions, the pH in your aquarium will vary a little over time. Adding make-up water and performing partial water changes alter the pH to some extent. Hard water typically yields an alkaline condition due to carbon dioxide reacting with carbonates and bicarbonates in the water. Day by day, however, excrement and other sediments plus respiration by fish and plants dictate a tank's pH. Good housekeeping helps maintain a more stable pH. Your fish will appreciate that.

Again, research may help you avoid tragedy. Some species require a particular range of acidity or alkalinity. They won't thrive outside that range.

You may easily test the water with inexpensive litmus strips or with a pH test kit available at your pet store. Then, if needed, you can adjust the pH with chemicals also from the pet store. Just be sure to follow the instructions carefully. Often, good aeration and filtration, together with good housekeeping, will eliminate the need for any chemical adjustment of your tank's pH.

Dissolved Oxygen
Just like you and I, our fish need gaseous oxygen to live. They can't breathe the oxygen that's bound with hydrogen to make water. Water absorbs gaseous oxygen from the air at the water's surface and turbulence increases this absorption.

Healthy plants give off oxygen during photosynthesis. However, photosynthesis occurs only when plants receive enough light. At night, or when the aquarium lights are off, plants consume oxygen during respiration. Therefore, an aquarist shouldn't depend on plants as an oxygen source. Plants, as nice as they are, won't replace an aeration/filtration system. In fact, unhealthy plants increase the oxygen demand in an aquarium. Microorganisms that decompose dead and dying plant parts consume oxygen. So do snails and every other living thing in the tank.

All of these organisms compete with your fish for dissolved oxygen. If there isn't enough oxygen to go around, your fish will lose the competition. Fortunately, oxygen in an aquarium is an easy factor to control.

Even the simplest aeration/filtration system, such as a corner box filter and air pump, will aerate an aquarium. In addition, good housekeeping eliminates dead plants and other decaying organisms. Vacuuming fish wastes and uneaten food from the substrate reduces bacterial growth while regular partial water changes increase your housekeeping effectiveness. Water changes help in other ways, as well.

A properly maintained aquarium not overstocked with fish probably will never lack sufficient oxygen.

Nitrate
High nitrate levels can kill fish. It seems that saltwater aquarists pay more attention to nitrate than do freshwater guys like me. But high nitrate levels in an aquarium can create an "unhealthiness" that is otherwise hard to diagnose.

We won't keep nitrates out of our aquariums completely. Nor should we even try. Nitrates commonly result from the decomposition of ammonia, not only a disinfectant but also a natural component of waste products. And nitrate is an important nutrient. The problem is that nitrate becomes toxic at high concentrations. Thus, our task is to keep the nitrate level low.

Four simple strategies help us accomplish this task.

1. Don't overstock the tank.
   
2. Don't overfeed.
   
3. Keep the tank clean: vacuum the bottom; remove dead plants, fish, and snails.
   
4. Perform regular partial water changes.

Did you notice a repeated theme in this article? Sensible aquarium maintenance helps produce a healthy balanced environment for your aquatic pets.