Saltcorner
By Bob Goemans
By Bob Goemans
Dear Bob,
Read with great interest a letter to your Sand Mail column in FAMA on the subject of using natural sunlight to light a reef aquarium. I must admit that I was a little disappointed by your reply, as I was hoping for some more specific information. You see I am in the process of building a 2500 liter tank from plywood and fiberglass, which I intend to be a reef. This tank is in it's own concrete floored annex to the house, with only the front glass visible in the house, and above it I have made a 2.4 by 1.2 meter skylight from a two-skinned product called Thermoclear which the retailers assured me will pass 80% of the light. This skylight is about 1.5 meters above the water level, (water will be about 750 millimeters deep) and I will line the walls of the room with silver foil to increase reflectivity. I will also use six 150 watt metal halide lamps for the later part of the day and the evening. I can't at this stage afford to run (or buy) stronger lights than these, and I feel that I will get a great deal of blue light through the skylight (after all the sky is blue) so don't plan to use actinics. I expect some loss of heat on cold nights and some heating problems in summer, but can use lots of ventilation to deal with that. I plan to heat the room rather than the tank to reduce evaporation and condensation). I live in Auckland New Zealand and our light is very bright and intense and strongly ultraviolet. Using this set-up I will also get considerable variation, clouds, dull days, very bright days, etc.
I saw in the Delbeek and Sprung Vol. 2 the pictures of the tanks at the Waikiki Aquarium using a mixture of natural light and halides but their web-site had no information on this subject at all. I have also followed the debate on using live sand either with a plenum or on the tank floor; alas all rather academic in New Zealand as neither live sand or live rock are available here owing to our very strict laws on imports of possibly environmentally dangerous organisms. Due to our small population and consequently small number of reef hobbyists it doesn't seem possible to bring enough pressure to change this, and with the Pacific Islands not far to the north it is very frustrating! We can get dead coral rock and sand, also a good variety of soft and hard corals, also fishes, so all is not lost!
I am planning on using only several large home-made protein skimmers to filter my tank. As I live fairly near the sea, natural water, and water changes are no problem. However, I would appreciate some advice on setting up a "live sand" bed or it's equivalent when one can't get real live
sand. All the sites I've found on the net assume the availability of live rock and sand.
Thank you,
Brian Timms
Auckland, New Zealand.
Hi Brian,
Let me first say that I've always wanted to visit New Zealand as I've seen many articles and photographs on its beauty and wonderful people. It sounds like a place I might never want to leave!
As for your email, I recommend requesting a chart showing what wavelength light passes through the product mentioned. If everything in the blue range and below is filtered out, and only the wavelengths such as yellow and red are allowed through, that does not benefit a reef system, no matter how bright it is. If light of 385 nanometers and above does pass through the product, then there may be sufficient blue spectrum to adequately trigger photosynthesis. And blue is the wavelength of choice when it comes to corals.
Yes, there is quite a lot of debate when it comes to sandbeds. Controversy is good for any subject, but needs to be voiced it in a professional and responsible fashion. After six years of researching sandbed microbial processes, a lot has been learned. One of those things has been the identification of microbial processes in sandbeds of different grain size and depth. Those findings have lent themselves to understanding system balance. This is of course, crucial to long-term success. Anyone can put together general system components such as sand, rock, pumps, and lighting and have something looking great for the short term. However, in my opinion, it's long-term success of the system that is all-important.
Those that understand and take into consideration the true foundation makers of a closed system, the microbial processes, are those that have more success. Simply fact, not fiction!
One of the more important findings centered on sandbed oxygen content. Where small amounts of oxygen existed, such as 0.5 to 2.0 mg/l, or what should be called the anoxic zone, bacteria reduced nitrate back to gaseous elemental forms. This is termed dissimilatory denitrification. Another plus in this area was that these bacteria were more than 30 times more efficient than those found in zones where there was less oxygen. This resulted in much better use of phosphorous and far less production of phosphate!
Unfortunately those that stress deep sandbed usage directly on the aquarium bottom are still clinging to the belief that their beloved method is superior to the Jaubert plenum method. They have expressed numerous conditions that range from plausible to ridiculous. Yet, fact is that when oxygen content is below the anoxic level, bacteria operating in that zone reduce nitrate back to ammonia/ammonium, no further. It is called the ammonification process or assimilatory denitrification (reassembly of ammonium, i.e., ammonification). Not only is another nitrogen product produced, the bacteria's inefficient use of phosphorous for energy results in an abundant amount of phosphate being leached into the surroundings. So in essence, deep sandbeds are more a never-ending circle/cycle of oxidizing the same nutrients over and over again! Unfortunately this mass of oxidation becomes greater with the age of the system. How long will it take for parts of that 'mass' to leach into the bulk water is anyone's guess. Of course, the influx of benthic invertebrate helps bring in additional oxygen in some areas and can help lessen the impact to water quality and system balance. But I would not want to hang my hat so to speak on that there will be sufficient influx and the right type invertebrate! I would prefer a method where oxidized nitrogen products in their elemental form are expeditiously returned to the bulk water.
As for using live sand, it is much more sensible to begin a system with live than dead/inert sand. Having a new system with more usable bacteria than nutrients gives the system a better chance for the microbes to become established before unwanted forms of algae! If the number of microbes are there, they can use whatever nutrients the new system has for growth and reproduction. If they are not there, those nutrients will lead to algae becoming established. So, if carbonate-like sand is available in any near-by shore areas, use it. If not, first establish a bed in the aquarium with no rock or animals. Use one of the many starting additives that help initiate the nitrification cycle. When that completes, then add the rest of the decor.
I hope this is helpful,
Bob
