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Low Bio-load Establishment of a Bio-Filter Using fish to establish a bio-filter humanely
In my youth, I remember going through a lot of fish in my first tank. After about two months, I finally ended up with a tank full of “survivors” that I kept for years. In those days, water changes were unheard of, since everyone wanted to preserve the “conditioned” water that was in the tank. Eventually, the survivors dwindled down to one or two, and were given away as I became a busy young adult with little time for a fish tank. Many years later, after a long academic career, I find myself in the fish section of a local pet store and the passion is re-kindled anew. Much has changed over the last few decades, all of it for the better. Tanks are better, filters are much better, and the knowledge of aquarium management is vastly better. The single greatest benefit of all has been the understanding of the nitrogen cycle in the aquarium, and the modification of filters to accommodate a bio-filter.
From my early experience, it is obvious that the nitrogen cycle was unheard of. Every beginning aquarist I knew went through the early fish death experience, now called the New Tank Syndrome. Every fish keeper I knew was unaware of the accumulation of nitrate, and was afraid to change the water in the tank. We had all heard that sometimes changing some of the water could perk up the fish, but we didn’t know why, and were reluctant to risk it. When a water change was done, more than 10% was considered dangerous to the balance of the “conditioned” water. Today we know that the nitrogen cycle, the generation of ammonia (NH3) by fish and decaying matter, the bacteriologic conversion of ammonia to nitrite (NO2) , and then conversion of nitrite to nitrate (NO3), is the most important factor of water quality in an aquarium. The predictable outcome of high ammonia levels, followed by high nitrite levels, that leads to fish death in a new aquarium (New Tank Syndrome), is caused by the absence of enough bacteria in the tank to efficiently convert ammonia and nitrite to the less toxic nitrate. These bacteria are present in tap water in small quantities, and will, with time, increase to effectively keep the ammonia and nitrite at near zero levels. While waiting for this bio-filter to develop, your tank is said to be “cycling,” or going through the period when ammonia and nitrite generation is in excess of bacteriologic conversion to nitrate, and this can be measured with a test kit to show elevated ammonia and nitrite levels. The effects of ammonia poisoning in fish are well documented. These effects include: extensive damage to tissues, especially the gills and kidney; physiological imbalances; impaired growth; decreased resistance to disease, and death. Nitrite poisoning inhibits the uptake of oxygen by red blood cells by altering the hemoglobin and causing methemoglobinemia. This problem is much more severe in fresh water fish than in marine organisms. The presence of chloride ions (CL-) appears to inhibit the accumulation of nitrite in the blood stream. When this pattern of high ammonia followed by high nitrite is done, your ammonia and nitrite levels will be zero on your test kit. The nitrogen cycle is still taking place in your tank, but the new tank cycle of highly toxic ammonia and nitrite levels is over. All that remains is the accumulation of nitrate, which can be controlled by regular partial water changes, plant growth, or both water changes and plant growth.
Traditionally, the bacteria responsible for the conversion of ammonia to nitrite were called Nitrosomonas bacteria. The Nitrosomonas species of bacteria do convert ammonia to nitrite, and are present in water treatment plants designed to treat waste water. The scientists at the Marinelab company studied aquarium bio-filters for a decade, in preparation to culturing nitrifying bacteria specifically designed to seed an aquariums bio-filter with all the bacteria needed for a complete and efficient nitrogen cycle instantly (Bio-Spira). In addition to Nitrosomonas bacteria, they found that Nitrosococcus bacteria converted ammonia to nitrite, and were present in larger quantities than Nitrosomonas. A third bacteria that remains unidentified and uncultured was also seen. None the less, when discussing the establishment of a bio-filter, you are likely to hear mostly about the biology of Nitrosomonas bacteria. Nitrosomonas bacteria will be present in the tap water you initially fill the tank with in small amounts. These bacteria are likely to be in an inactive or dormant, free floating state, that won’t do your tank much good. However, In the presence of ammonia, Nitrosomonas will reactivate, adhere to the substrate in your tank and filter, and begin to metabolize ammonia. Using ammonia for energy is not terribly efficient, so the Nitrosomonas bacteria have a slow growth rate. Typical bacteria might double in population every 20 minutes, but Nitrosomonas require 7 hours.
Nitrosomonas growth is dependent on several water quality parameters. The following data pertains to Nitrosomonas bacteria cultured for sale by Fritz Industries, Inc., and for informational purposes we will assume it probably applies also to the bacteria in your tank. The pH is very important, with a pH of 7.8 to 8 being optimal. Nitrosomonas growth is severely restricted by a pH of 6.5, and nitrification is stopped at a pH of 6. I am not recommending that you attempt to adjust your water pH with chemicals while establishing a bio-filter, since rapid swings in pH are likely to result. Just be aware that the process might be slower if you have neutral to acidic water. If your pH plunges while establishing a bio-filter, water changes to raise the pH are likely necessary. Temperature is also a factor. Optimal temperature for Nitrosomonas growth is 77 to 86 degrees, which fortunately coincides with the temperatures we are likely to keep our tropical fish. For aquarists keeping cold water tanks, Nitrosomonas growth is reduced 50% at 64 degrees, 75% at 48 degrees, inactivation at 39 degrees, and the bacteria die at 32 degrees. They also die at the high temperature of 120 degrees. Phosphate is also required for Nitrosomonas, and unless you are using distilled or reverse osmosis water, it should be present in enough quantities. Dissolved oxygen is also required since it is aerobic metabolism, but I would think your fish would show signs of oxygen deficiency long before Nitrosomonas would. However, an under-gravel filter could harbor anaerobic bacteria whose byproducts can be toxic to nitrifying bacteria if water flow was reduced or stopped.
The bacteria that metabolize nitrite to nitrate are traditionally referred to as Nitrobacter. Once again, the scientists at Marinelab have determined that another bacteria, Nitrospira, is more active at nitrite metabolism. Now you know why their product is called Bio-Spira, proudly advertising their research. Regardless, when you are discussing nitrite conversion to nitrate, you are most likely to hear about the biology of Nitrobacter. Nitrobacter is even more slow growing than Nitrosomonas, requiring 14 hours to double in population. Nitrobacter grows best at a slightly lower pH of 7.3 - 7.5. The temperature, phosphate, and oxygen requirements are similar to Nitrosomonas bacteria. Nitrobacter is able to metabolize energy sources other than nitrite, and does not have a dormancy mechanism.
It is not difficult to find information on the Internet for establishing a bio-filter by a variety of methods. As conscientious fish keepers, filling a tank and adding a full bio-load of fish, then letting the New Tank Syndrome play itself out is not an option. Much of the Internet information is dedicated to establishing a bio-filter without the use of fish at all. Methods of adding food or dead shrimp that is allowed to decay and produce ammonia in a tank with no fish have been described. Adding pure ammonia to the fishless tank has been around for a long time as well. I have a book copyrighted in 1985 that describes adding pure ammonia to a fishless tank, but the practice has become more widespread since the late 1990’s, when the internet became such a useful tool to disseminate information. While fishless bio-filter development is efficient and spares your pets the exposure to toxic substances, your fish tank will really be a giant test tube and not a fish tank for two to 6 weeks while you wait for bacterial growth. I wonder how many people new to the hobby are willing to go through a fishless process for such a long time? And if difficulties occur, are they likely to stick with the hobby? For this reason, I believe it is also important to discover ways to establish a bio-filter humanely, with the use of fish. The development of Bio-spira is a fantastic tool for the new aquarist. The only problem is that Bio-spira may not be available to all aquarists, its cost may be prohibitive, and if the Bio-spira culture is mishandled or damaged, New Tank Syndrome will occur. Therefore, it is also important to establish safe and effective methods the old fashioned way, by adding fish slowly.
I have established a bio-filter in my 55 gallon freshwater tank using fish without subjecting the fish to ammonia or nitrite spikes on two occasions. With my most recent attempt I was a vigilant observer and kept detailed notes. The secret is a low initial bio-load combined with a high dose of patience! During my “Low Bio-load Project,” I performed twenty negative ammonia tests, nineteen negative nitrite tests, and thirteen negative nitrate tests, over 40 days. That’s a lot of negative testing, and why you need a lot of patience. During those forty days I added 6 Zebra Danios and four Platies on day one in a 55 gallon tank. I fed sparingly (flakes consumed in under 2 minutes, none getting down to substrate), and when ammonia and nitrite were still zero after 12, days I added three more Platies. I had now reached my target bio-load of one Danio or Platy per 5 gallons (about one inch of fish per 5 gallons). I continued to feed sparsely once or twice a day, and did not add any more fish until nitrate was detected on day 40. I was never able to detect ammonia with an Aquarium Pharmaceuticals liquid freshwater master test kit, lower limit of 0.25 ppm. I was never able to detect nitrite with the test kit lower limit of 0.25 ppm. I was able to detect nitrate at the lower limit of 5 ppm on day forty, which signaled the success and end of the project. I did perform a gravel vacuum and 15% water change on day 33, since I would never normally skip gravel vacuums for more than a month in a tank. During the project, I had one male Platy that was poorly feeding beginning on day 24, who disappeared on day 34. I never found its remains.
With a 55 gallon tank, I believe it is safe and humane to establish a bio-filter using fish if done correctly. To follow my example, you would add up to one inch of fish per five gallons over a two week period. Then you would feed sparsely, and add no more fish until nitrate was seen to increase, and ammonia and nitrite are zero. I still think you would want to start with hardy fish just in case, and to follow my example exactly you would choose Danios, Platies, or some of both. I think you should choose small fish, since an inch of Blood Parrot is not the same bio-load as an inch of Danio. I would think that there would be variation from tank to tank, since your “sparse” feeding may be a different amount than mine. Furthermore, the amount of nitrifying bacteria that you start out with will likely be different from tank to tank, and city to city. As we have discussed, temperature and pH differences can affect results, and your tank might be different than mine (78 degrees, pH=7.8). Finally, I do not think you can extrapolate my experience with a 55 gallon tank to include smaller or larger systems. It very well might be that smaller systems need and even lighter initial bio-load (one inch per 7 gallons?), or that larger systems might tolerate a larger initial bio-load. I do believe that as dedicated aquarists, we could explore and answer these questions in order to provide better guidance and protocols to offer newcomers to the hobby. I would encourage all to replicate or expand upon my Low Bio-load Project to verify and increase our knowledge. And most of all, I believe you will enjoy your new tank right from the start, because it has fish in it!
Tom K
Internet Sources for this Article:
http://www.marineland.com/science/nspira.asp http://www.bioconlabs.com/nitribactfacts.html http://article.dphnet.com/cat-01/naturewonders2.shtml http://article.dphnet.com/cat-01/naturewonders3.shtml http://article.dphnet.com/cat-01/naturewonders4.shtml |