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8.10 NITRITE:
As already recommended, nitrite levels should be zero ppm at all times. If your testing determines any level of nitrite whatsoever, your biological filter is not operating optimally. Very low amounts of 0.01 to 0.1 ppm may be an indication that some amount of denitrification is taking place somewhere in the system. This may not be a cause for concern but you should try to eliminate the reason for it. Nitrite interferes with the oxygen metabolism and is therefore extremely noxious.
If you determine that nitrite is higher than those values, you may have a similar situation as the one described under 8.9, Ammonia. Review what you have done in the last week or two, and determine whether such may have brought about the nitrite problem. If not, your biological filtration may be too small for the amount of livestock that you keep in the tank. Again, increase the amount of such biological filtration.
One often overlooked cause of lower water quality is dirty mechanical filters. Clean them and determine whether that improves the situation. It often will.
Because ozone neutralizes nitrite by chemically breaking it down further, you may wish to experiment with increasing the amount of ozone that you are injecting into your protein skimmer or ozone reactor. This may or may not help. It will not if your biological filtration level is clearly too low. In such a case you need to resort to providing more biological filtration to the tank. But if the presence of nitrite was due to a temporary increase in organic material that your filters can normally cope with, but are still adjusting to, ozone will solve your problem.
Nitrite that appears a few days after adding new animals to the tank should not be present longer than 7-10 days, and then only in very small amounts. If it is, you must do something about it. Perhaps those last few animals that you added just taxed the system too much.
Because many hobbyists assume that once the cycle is passed they no longer need to test for nitrite since they have a biological filter to take care of that problem, nitrite is frequently overlooked as a cause for low water quality levels. For example, we may get a call at Aardvark Press from a hobbyist stating that all is OK with the tank, he or she tested both nitrates and phosphates and both are really low, but the redox potential just does not want to go up. Such is often a sign of under-filtration on the biological side, and the presence in the water of nitrites. But since the hobbyist did not test...
8.11 NITRATE AND NITROGEN NITRATE:
Unlike phosphates, hobbyists have been testing for the presence of nitrates in their tanks for years. As far as I can remember in fact. Nitrates have been recognized as a problem compound in fish-only tanks by many authors and hobbyists are, as a result, aware that such levels must be kept within certain ranges.
What is not as clear, is that fish-only tanks and reef aquariums do not place the same requirements on the water quality. Far from it, reef tanks need much higher levels of water purity, and nitrate levels in reef tanks (and many other compounds as well, not just nitrate) need to be much lower than in fish-only ones. This poses a problem insomuch as a lot of the literature that hobbyists read was intended to be supportive of the hobbyist who was only keeping fish. Not realizing this, many hobbyists still assume that nitrate levels advocated for such tanks apply to their own, when such is not so at all.
As a result, nitrate levels found in reef tanks are usually much higher than what they should be, mainly because the hobbyist feels that such levels are acceptable, having read so in books, magazines, and so on. Until more literature that deals with reef tanks becomes available, this mistake will be made over and over again.
Water quality parameter demands in reef tanks are much more stringent, and nitrate, and many other levels, must be considerably lower than what one finds recommended as acceptable for fish-only tanks.
My recommendation is to keep nitrate levels below 5 ppm of NO3, or 1 ppm of N-NO3, much lower, in my experience, than the levels most hobbyists keep their reef tanks at.
If the nitrate level in your tank is too high, you can resort to any of the following three methods, either on their own, or in combination, the latter being done by many hobbyists:
Of course, cutting down on feeding, lowering the amount of lifeforms in the tank and using a more efficient protein skimmer will greatly help as well.
It can be demonstrated that corals open much wider in tanks with low levels of nitrate (and phosphate), and you can see so for yourself by lowering them in your own tank. It is a time consuming effort and one that requires perseverance. Do not expect immediate results with any of the three methods recommended. All will take weeks for any significant differences to become apparent. But they will, if you keep at it. Denitrators for example require 4 to 5 weeks before you will see any significant changes in nitrates in the tank. Patience is, unfortunately, not always a trait the hobbyist excels at. This is not meant in a derogatory way, but it is a fact with the majority of hobbyists that I have been in touch with, and that is quite a few.
We refer to two types of nitrate levels in this section: NO3 and N-NO3. NO3 is the highest of the two measurements and, obviously the one that you must watch, because it is the most complete type of measurement. N-NO3 is always the lowest as it measures only partly what the total NO3 content of the water is. The conversion is as follows: 4.4 times N-NO3 = your real NO3 level. For example: 10 parts of N-NO3 is the same as 44 parts of NO3.
10 parts per million may seem in the correct range to many hobbyists, but since you now know that such is only part of the total NO3, and that the real total is 44 parts per million, you can well imagine how easy it is to believe that the water quality is fine when in fact it is not. Many hobbyists make that mistake because they are not aware of the difference between the two, and because most tests available to the hobbyist measure, in fact, N-NO3 and not NO3.
Keeping your tank's nitrate levels low is one of the major objectives you should focus in on, and should also be high on your list of priorities. The approach should be twofold:
1. Do not add anything to the tank that artificially increases them,
2. Take all steps necessary to ensure that naturally occurring nitrates are efficiently reduced.
Nitrate can enter the tank artificially through the salt and water source you use, in the same manner as phosphates can. Both must be tested to ensure that such is not the case. Review your feeding techniques and reduce the quantities fed if your nitrate level is now high. Do not feed several times a day. Remove all dead or dying algae as soon as you notice them. Letting them decay, even if that is what is happening, will increase your nitrate levels for sure. Do not use old coral rock, from other tanks, unless you first scrape off all dead material that may still be on it, and after rinsing it thoroughly and several times. Clean all your mechanical filters regularly. Be especially careful with fertilizers for macro-algae. Test them before you add them to the tank to make sure that they do not contain nitrates and phosphates. Use an efficient protein skimmer, one that really removes organic material from the water, because once the skimmer has removed it, it can no longer break down and increase nitrates.
8.12 SALINITY, SPECIFIC GRAVITY:
Keep the salinity at 35 parts per thousand. Such is the level around most natural reefs and it is, therefore, what most of the animals that you keep in your tank are accustomed to. If they do fine at that salinity around the reef, why change it?
Many hobbyists measure the specific gravity rather than the salinity. The specific gravity (s.g.) that I suggest, which corresponds to 35 ppt salinity, is 1.0234 at 77 Degrees Fahrenheit. Because the s.g. is temperature dependent, you must always match the s.g. up with the temperature at which you are measuring. Conversion charts for specific gravity can be found in, for example, Martin A. Moe's: _The Marine Aquarium Handbook, Beginner to Breeder_ (Green Turtle Press).
If you do not have a really accurate hydrometer, use a salinity test such as the one sold by LaMotte Chemicals, instead. Alternatively, use a refractometer that gives a salinity reading as well. Such units cost around $300.00 and are worth the investment. They make the test so easy that you are more likely to perform it.
All one does is place a few drops of aquarium water on the front of the unit, look through the visor, and read the salinity on the scale. They can be ordered from companies such Cole Parmer, Markson's, Extech, and several others. All these companies have (800) numbers which you should be able to get from directory assistance in your area, or from the (800) directory assistance operator. TAT also sells such units.
Because of evaporation, the salinity in your tank will change continuously. Salt does not evaporate, only water. As a result, the salinity has a tendency to go up. To counteract this fresh water is added to the tank on a regular basis. This brings the salinity back in line. The more frequently the topping-off occurs the less pronounced the variations in salinity will be.
As I have already pointed out several times, one of the keys to success with a reef tank is keeping the water chemistry as stable as possible. Top your tank off every day, or set up an automatic system to do so, either as a drip method or using a small dosing pump, combined with a timer, if necessary, to reduce its output further.
Some articles suggest that you should keep the salinity at a lower level, as such would protect your tank from parasitic disease outbreaks. Levels as low as 1.019 are recommended. I do not recommend this approach in reef tanks at all. I have not found it to work for any length of time anyway, because parasites can adapt to a changing environment just as well as the fish you keep in it. Moreover, invertebrates and corals do better at the salinity that they are accustomed to around natural reefs.
Should you keep the salinity higher? Depending on which type of tank you run, you may wish to increase it somewhat. This is especially so if you keep a lot of Red Sea lifeforms. Do not increase it over 37 ppt though if your tank is filled with animals of mixed origin.
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