Hi all, thought I would share an important piece of info with you we discovered long ago. Aquaculture farms have a lot of the same problems Hobbyists do. Filtration issues, disease concerns, water quality and low oxygen. Hopefully, this info may help other Aquarists to solve some of their problems. Understanding the importance of proper lighting, the 24 hour photo period in your refugium and the fact that most algae are beneficial in producing oxygen on demand. Some people light the refugium 24/7 and some give the fuge a break once a month. I let my fuge sleep about once a month. the rest of the time its lit. Oxygen in water comes from two sources: photosynthesis and diffusion from the air. The most important source is photosynthesis, which is the process plants use for manufacturing food. In the presence of sunlight, plants (especially algae) add oxygen to water as a by-product of photosynthesis. At night, no oxygen is produced, but respiration of algae, fish and bacteria continues to remove oxygen from the water. Most of the time there is a desirable balance between how much oxygen is produced and how much is used, but under most conditions, the balance can be upset, and the oxygen concentration becomes low enough to stress or kill fish. The amount of oxygen in tank water can vary considerably from hour to hour. Typically, however, oxygen concentrations are lowest at dawn and highest during late afternoon. The amount of oxygen water can hold is dependent upon atmospheric pressure, salinity and temperature. Water can hold less oxygen as altitude increases. The oxygen level in a reef tank in Nevada may be different than the oxygen level in a reef tank in Florida. water can hold less oxygen as it becomes warmer respiration rates of both plants and animals increase with the warmer water, so more oxygen is used. normally, reef tanks run about 80 degrees all the time. Nevada is higher altitude than the natural sea level. Causes of oxygen depletion The most common oxygen problem occurs when consumption by respiration exceeds the amount of oxygen produced through photosynthesis and diffusion from the air. Algae grow in large quantities as a result of heavy fish feeding or tap water nutrients. As the quantity of algae increases, it accumulates closer and closer to the surface to gather sunlight and increasingly shades the lower depths. As a result, most of the oxygen is produced near the surface, leaving a large volume of water below the first 2 to 4 feet deficient in oxygen production. Eventually, oxygen produced during the day is less than the demand for oxygen during the night, resulting in possible death or undesirable stress on fish. thanks, George.