Yes, sir, sometimes you can cycle a new aquarium simply by adding sufficient live rock and/or live sand. There will normally be some die off of the encrusting organisms on the live rock, and the resulting decay is often enough to provide the ammonia that’s needed to sustain a burgeoning population of beneficial nitrifying bacteria. But precured live rock from your LFS may not experience a significant die off, and therefore cannot always serve as the ammonia source while the aquarium is cycling. If you have never observed an ammonia spike in your new tank, then that is the case with your aquarium, and you’ll have to provide another source of ammonia to feed the biofilter and build up as large a population of Nitrosomonas and Nitrobacter anaerobic bacteria as possible.
The fact that there hasn’t been an adequate ammonia spike and an ongoing source of ammonia to nourish the beneficial bacteria in your new tank may have set back the cycling process a bit, but it should recover quickly once you begin providing ammonia, and there are a few things you can do to further accelerate the cycling process. For instance, you can increase the aeration and the temperature in the aquarium while it is cycling. The beneficial nitrifying bacteria (Nitrosomonas and Nitrobacter sp.) that convert ammonia to nitrite and nitrite to nitrate are all aerobic or oxygen-loving microbes, so their population will increase faster if there is a high level of dissolved oxygen in the aquarium. Adding an airstone to provide better surface agitation and promote efficient aeration and oxygenation while your tank cycles should be helpful.
Secondly, I would raise the temperature in your aquarium to around 80°F while it cycles. Bacteria multiply faster at warmer temperatures, so raising the water temperature should help stimulate faster growth of the beneficial nitrifying bacteria as well. (Don’t forget to reduce the aquarium temperature back to normal once it’s finished cycling so that it’s optimal for your seahorses.)
There are a number of different ways to seed the tank with bacteria initially and feed it with ammonia so cycling can proceed. Two popular methods are the fishless cycle, which I recommend, and the use of hardy, inexpensive (i.e., expendable) fish to produce ammonia and cycle the aquarium. Often used for this method are marine damselfish or mollies, which can easily be converted to saltwater. Both are very hardy and generally survive the cycling process, but I find this method to be needlessly hard on the fish and exposing them to the toxic ammonia and nitrite produced during cycling certainly causes them stress. Damselfish are far too aggressive and territorial to leave in the aquarium afterwards as tankmates for seahorses. Mollies are a possibility, but they really look out of place in a saltwater setup.
So all things considered, I recommend cycling your tank without fish. It’s really very easy. To use the fishless cycle, you need to add something else that will increase the ammonia level so the nitrifying bacteria can build up. I like to use a piece of cocktail shrimp (regular uncooked eating shrimp from the grocery store) or two and leave this in the tank to decay during the whole cycle. The decaying shrimp produces plenty of ammonia to kick-start the cycling process.
After about 3 days after you add the shrimp, you will notice a spike in ammonia levels until the Nitrosomonas bacteria build up enough to break down the ammonia. When that happens, you will notice the ammonia levels rapidly dropping. (If for some reason your ammonia does not hit the top of the charts initially, you may want to add another piece of shrimp.)
The byproduct of ammonia is nitrite, and during this stage of the cycling process, as the ammonia falls, you will have a corresponding increase in nitrites until the population of Nitrobacter bacteria builds up. Nitrite levels will then fall as the Nitrobacter convert the nitrite to nitrate.
It is important to use your test kits every day or two when cycling your tank this way in order to monitor the progress of the process. As described above, normally at first you will see a rapid rise in ammonia levels with no detectable nitrite or nitrate. Then, as Nitrosomonas bacteria begin converting ammonia to nitrite, the ammonia levels will fall and nitrite readings will steadily rise. Nitrite levels will peak as the ammonia drops to zero. Next, Nitrobacter will begin converting the nitrite to nitrate, and your nitrite readings will fall as the level of nitrate rises. Finally, after the nitrites also read zero, you are ready to stock your tank. At this point, your ammonia and nitrite levels should both be zero, nitrates will be building up, and algae will usually begin to grow. This will tell you that your biofilter is active and functioning properly, and that you can now safely begin stocking the tank. It generally takes about 3-6 weeks to cycle a tank this way from scratch. But if you’re using live rock and live sand, along with pre-mixed, aged saltwater, you can expect a much faster cycle. Just monitor your tank as suggested above and you’ll know when it is safe to add your cleanup crew and begin stocking the aquarium.
In short, a few of the things that are known to accelerate the nitrogen cycle and establish the biofiltration more quickly are to increase the aeration/oxygenation in the new tank, raise the temperature of the water to allow the population of nitrifying bacteria to grow faster, and to feed the biofilter with ammonia you add to the water drop by drop.
Many times the best way to accelerate the cycling process is to feed the biofilter directly with ammonia drop by drop, as described below.
The best way to accomplish this is to feed the nitrifying bacteria directly with ammonia that you add to the tank drop by drop yourself, which has a couple of worthwhile advantages. First of all, the amount of ammonia you add daily is far greater than that the amount of ammonia hardy damsels or mollies can produce nature’s way as waste products. The excess ammonia means the bacterial colonies can grow faster and produce much larger populations of Nitrosomonas and Nitrobacter bacteria by the time the cycling process is complete (Cow, Jan. 1999). The result is that your tank cycles faster, typically in 10-21 days as opposed to 4-6 weeks for more conventional cycling methods, and the tank can ordinarily be stocked at capacity once the cycle is completed (Cow, Jan. 1999). As an added bonus, there isn’t the unpleasant odor of putrefaction that can sometimes become a major annoyance when using decomposing cocktail shrimp as the ammonia source.
To cycle your tank this way, simply add ammonia drop by drop, keeping track of how many drops you’ve added, until it produces a reading of ~5 ppm on your test kit (Cow, Jan. 1999). Then continue to add exactly that many drops of ammonia each day thereafter until you begin to see detectable levels of nitrite. Then once nitrite readings begin to appear on your test kits, cut back the amount of ammonia you add to 1/2 the original amount, and continue to add a half dose of ammonia each day until the cycle has finished and you stock the aquarium (Cow, Jan. 1999).
It is important to use your test kits every day or two when cycling your tank to monitor the progress of the process. One benefit of fishless cycling method is that it produces an immediate ammonia spike, which accelerates the cycling process accordingly (Cow, Jan. 1999). So at first you will see a rapid rise in ammonia levels with no detectable nitrite or nitrate. Then, as Nitrosomonas bacteria begin converting ammonia to nitrite, the ammonia levels will fall and nitrite readings will steadily rise. Nitrite levels will peak as the ammonia drops to zero. Next, Nitrobacter will begin converting the nitrite to nitrate, and your nitrite readings will fall as the level of nitrate rises. Finally, after the nitrites also read zero, you are ready to stock your tank. At this point, your ammonia and nitrite levels should both be zero, nitrates will be building up, and algae will usually begin to grow. This will tell you that your biofilter is active and functioning properly, and that you can now safely begin stocking the tank (Fenner, 2003b). It generally takes anywhere from 10 days to 3 weeks to cycle a tank this way from scratch using the fishless cycling technique (Cow, 1999).
When cycling your tank with this method, it is advisable to perform large water changes (70%-100%) before adding any specimens to the tank in order to lower the elevated nitrate levels it produces and correct the pH (Cow, 1999). Otherwise, it can be difficult to bring the nitrate down to manageable levels again after the tank is stocked. Ammonia is a powerful base, so adding ammonia changes the pH of the water substantially, making it more alkaline (Warland, 2003). A large water change will reduce nitrite levels and lower the pH back to normal after the tank has cycled.
When changing the water, avoid using dechlorinators that also sequester ammonia, the so-called ammonia quellers, since we are relying on high ammonia levels to feed the bacteria colonies. When performing water changes during a fishless cycle, stick with simple chlorine neutralizers that don’t affect ammonia levels (Cow, 1999).
Not just any ammonia will do when cycling the tank this way. The ammonia used for this purpose should be free of surfactants, perfumes, and colorants (Cow, 1999). ACS grade ammonium hydroxide is best but may be hard to find. Pure or clear ammonia will do nicely and the best places to get it usually hardware stores or discount grocery stores. Many times it’s the off-brands or little-known, no-frills generic brands that work best (Cow, Jan. 1999).
When you find a likely candidate, be sure to check the ingredients on the bottle of ammonia. The good stuff will simply say Clear Ammonia (or Pure Ammonia or 100% Ammonia, or Pure Ammonium Hydroxide), and list no additives (surfactants, coloring agents, perfumes, etc.; Cow, 1999). If the bottle does not list the ingredients or lists added ingredients like those specified above, pass it by and take your search elsewhere. When in doubt, administer the shake test. Shake the bottle vigorously — ammonia that contains surfactants will foam up, but the good stuff suitable for fishless cycling will not (Cow, Jan. 1999).
When cycling the tank this way, it’s important to remember that the high levels of ammonia involved are toxic to all fish and invertebrates, so you cannot use ammonia to establish the biofilter if there are any inhabitants present in the aquarium (Warland, 2003).
Best of luck cycling your new aquarium and building up an enormous population of nitrifying bacteria to carry out the biological filtration, arcprolife!