The following excerpt has been taken from the Reef Notes series of books featuring questions answered by Julian Sprung and have been printed here with his full permission. Please check back frequently as we will be adding different topics on a regular basis. All previously printed topic will be held in an archive link.

Topic: Temperature
The temperature of a successful aquarium should remain stable over the course of a day. A daily variance of plus or minus one degree Farenheit is perfectly acceptable, but larger variance can stress fish sufficiently to lower their resistance to common diseases such as "ICH" and "Velvet" Cryptocaryon and Amyloodinium. This temperature induced weakness in marine fish has been explained ni the literature as being an artifact of relatively stable temperates found on coral reefs where tropical marine fish come from, compared to the wider variance in temperature occuring in lakes and wetlands where many freshwater fish come from. I don't believe this explanation because I have experinenced dramatic temperature changes on coral reefs in shallow water with the change of tides, an in deep water with thermoclines. I can't explain why unstable temperature is such a stress in closed system aquaria compared to the natural environment, but I know it is. A heater or chiller is very helpful in the maintenance of the temperature. Simply air conditioning or heating the room that the aquarium is in, however, may sufficiently maintain the temperature in smaller systems. As I just explained, temperature fluctuation is stressful to fish. Invertebrates and plants, however, are far more tolerant of fluctuations in temperature, but they must be maintained within a range of temperature. A tropical marine aquarium must be maintained no cooler than 68 degrees Farenheit nor warmer than 80 degrees Farenheit. The ideal temperature is about 74 degrees.

The saturation of oxygen in the water relates particularly to the high end of this temperature range. Oxygen is less soluble in warmer water, so it si in shorter supply in a warm aquarium. In the natural environment, the crashing of waves, flow of tides, and photosynthesis by algae all contribute to the maintenance of a dissolved oxygen level near or above saturation both day and night. In an aquairum the oxygen level may rise above saturation during the day because of photosynthesis, but it often falls dramatically at night as a result of respiration in the absence of photosynthesis, and slower gas exchange in an aquarium compared to the natural environment that has the advantage of wind and waves. This is why organisms may thrive at much higher temperatures in the natural environment than they do in aquaria.