| NetPets® |
8.8 DISSOLVED OXYGEN LEVEL:
Oxygen is a necessary and life sustaining element that all lifeforms in the aquarium including the bacteria in your filter need, and they need it in large amounts and all the time. Maintaining high levels of dissolved oxygen, therefore, reduces the stress on all such lifeforms because they have to labor less to get it. Because the bacteria in your biological filter require lots of oxygen as well, maintaining high level of D.O. ensures optimum biological filtration.
In light of this it would be totally counter-productive not to make sure that D.O. levels are high. How high? Around all natural reefs the dissolved oxygen level during the day, when photosynthesis is really at its peak, is at saturation or higher. Such is, of course, what you must try to achieve in your own tank. Why do anything different than what is tested around natural reefs?
Saturation is a somewhat misunderstood concept. Water can absorb oxygen from the air above the tank, or from air injected in the biological chamber, but there is a natural, chemical that is, limit to the amount of oxygen it can hold in solution. That level is called the saturation level. The saturation level is also dependent on the temperature of the water. At lower temperatures the amount is higher, and at higher temperatures the amount is lower (an inverse relationship). Running your tank at 75-76 deg Fahrenheit, rather than at 79-80 deg, therefore, naturally increases the mg/l of dissolved oxygen that can be present in the water.
Using oxygen reactors, devices inside of which air and water are maintained under over pressure, usually between 3 and 6 psi, will also result in higher levels of dissolved oxygen, because air contains around 21% oxygen. Such reactors are described in a later chapter and are usually installed in tanks where the filtration is somewhat too small, or where the load is high, or more often than not, both.
Any device installed on the tank, any method used, any practice adhered to, that increases the dissolved oxygen level of the tank is a beneficial one and is to be recommended, as it reduces the stress on all lifeforms. Less stressed lifeforms means better looking tanks.
On the not so positive side, many processes that take place in the aquarium constantly and continuously reduce the amount of oxygen available. Metabolism, fish respiration, biological activity, decay, unclean filters, small amounts of hydrogen sulfide, overfeeding, overcrowding, and so on, are all ways to describe processes that lower the dissolved oxygen in the water in your reef tank. All must be avoided if you are going to have an aquarium that looks vibrant.
Is oxygen oversaturation dangerous? Some have alluded to the fact that while injecting pure oxygen in an oxygen reactor, their animals reacted negatively. Such is correct insomuch as pure oxygen has a very high redox potential, or said differently, a very high oxidative power.
Too high an oxidative water quality will result in the same harmful effects one would have if ozone were present in the tank itself. Scuba divers will understand this much better, since breathing pure oxygen, especially at shallow depths, will cause the same deleterious effects. It surprises me that the test was even conducted. We do not recommend the use of pure oxygen and never have. At best, enriched air can be injected into a reactor, without any damage occurring. Do not return the water from the reactor directly to the tank, and do not return it to the biological chamber either, it is too aggressive and needs to be mixed with the rest of the tank water first. Return it to the sump of the trickle filter.
Several dissolved oxygen tests are available. LaMotte Chemicals, Chemetrics, and a few others are offered for sale in pet shops and by companies specializing in reef tank equipment. Get one. Testing for dissolved oxygen levels is an important aspect of being able to interpret the quality of the water in your tank. Most tests are based on the old Winkler method which was first developed in the 1880's, and that method is still advocated by many national organizations concerned with the environment. Electronic meters are available from scientific supply houses as well, but are rather expensive. A quality meter and its electrode can easily cost around $800.00.
Because the level of oxygen dissolved in the water is so important you must ensure that you do everything possible to keep it at as high a level as you can. This includes :
Quite a number of points to watch out for, and quite a number of husbandry steps to consider. But they are all to the benefit of what you already have in the tank and what you plan to add at a later date. Do yourself and the tank a favor, adhere to a regular and complete maintenance schedule. You will have far less problems with your tank than someone who doesn't.
Some authors recommend the use of hydrogen peroxide (H2O2) to deal with oxygen deficiencies quickly. Don't do it. I have tried it many times and have always experienced very negative results, especially with corals. Fish can take the treatment if you do not overdose, but invertebrates and corals react extremely adversely. It may seem like a quick-fix, but it is bound to give you more problems that you bargain for.
Last but not least, what is an acceptable D.O. level? As indicated, temperature is a factor that influences the level, and so is the organic load of the tank. If your test results in a level of less than 6 mg/l you must look for the cause(s) and correct them immediately. If you follow the list of steps on the previous page, you should be able to maintain a level higher than 7 mg/l, preferably higher than 8.00 mg/l. Higher levels are better.
8.9 AMMONIA:
No ammonia should ever be present in a reef tank other than during the period of its filter's maturation. During the cycle, as it is called, ammonia and ammonium ion will appear as long as your filter is not populated with enough bacteria to deal with the lifeforms load in the tank, and the by-products chemically and biologically developing as a result of their metabolism and your feeding.
Ammonia/ammonium is much more toxic at higher pH levels, which is the reason that it is a bigger problem in salt water tanks than it is in freshwater aquariums. Why is this so? In water of higher pH levels, ammonium ion, usually present as ammonium hydroxide and relatively less toxic, changes to ammonia gas which dissolves very easily and is much more toxic.
The presence of ammonia at anytime other than during the cycle should be a real reason for concern. It means that your biological filter is not performing as it should, or that it is too small. That, in turn, may be an indication that your tank is overcrowded and that you must either remove animals (unlikely in my experience) or that you must increase it biological filtration capacity to enable it to deal with the amount of pollution created by all the animals you stock in the tank.
Increasing the biological filtration ability of your filter can often be achieved by resorting to a better filtering medium, for instance one of the many plastic filtering media now available. You may wish to change from an older type of filtering material to a much newer one, one that promotes more gas exchanges. It does not always mean that you must buy a new filter. You may also need to blow air in the biological chamber, if you are not already doing so.
Other methods include adding a canister filter, and fill it with a high quality medium to increase the amount of biological filtration that can take place. You may also consider adding an oxygen reactor, as such devices also provide biological filtration. The point is, no amount of ammonia is acceptable. If any is present, you must do something about it immediately. Talk to your pet store, to a friend who is also in the hobby, or call one of the reef specialist companies, and see if they can help you. Read other books, and think the problem through. You will probably come up with a solution that is not too difficult and not too expensive to put into place. You may also want to read my 2 other books for more ideas on what can be done.
Before deciding that major changes are necessary, review what you have done or changed to the tank in the last week or two. Have you added a number of animals, did you use any type of medication that may have interfered with the filter's performance, and so on. If you can attribute the presence of ammonia to any such change you may not be as bad off as you first thought. Water changes, and patience, may just solve your problem, and hopefully no damage will have been done to your animals.
| Back to Table of Contents | Back One Chapter | Top | Next Page |
 NetPets® Main Page |  The Fish Center |