The recommended stocking density for large seahorses of average size such as Mustangs and Sunbursts (Hippocampus erectus) is one pair per 10 gallons. So, theoretically, your 120-gallon aquarium could safely house a dozen pairs of large seahorses, or 24 adult individuals when stocked to capacity. But, of course, it’s always best to avoid stocking aquariums to their carrying capacity, and if you’re new to seahorses, you will have much greater success if you keep your tank understocked to provide yourself with a bigger margin of error while you are learning the ropes and gaining valuable experience with these amazing aquatic equines. My best advice would be to start slowly and very gradually build up your herd over a period of many months.
Yes, many gobies make compatible tankmates for seahorses. See the discussion thread on this page titled "Fish compatibility" for a more comprehensive list of the types of gobies that usually do well with seahorses, as well as some precautions that must always be observed when keeping other marine fish with seahorses.
No, mom, you do not need any sand sifters in your seahorse tank. They are necessary for Deep Live Sand Beds, but the substrate in your seahorse tank will be a shallow sand bed that’s just 3/4 -1 inch in depth. No sand shifters are needed for a live sand bed that is this shallow, since the sand will remain well oxygenated from top to bottom without their help.
In your case, be sure to avoid the sand sifting starfish altogether, mom. For one thing, keeping a sand sifting starfish is problematic in a small 20-gallon aquarium. They are difficult to keep alive and do best in large aquaria (55 gallons and up) with a deep live sand beds that have been well-established and therefore have built up a large population of meiofauna. There just isn’t going to be an enough fodder for a sand sifting starfish to thrive in a 20-gallon aquarium with a shallow sand bed, particularly a newly established tank. I wouldn’t consider adding a sand sifting starfish to any aquarium until it had been up and running for at least six months or a year. In your case, I wouldn’t get a sand sifter at all since they are not needed in an aquarium with a sand bed that’s just an inch or so deep, and your new seahorse system is really too small to support one.
But you do need a cleanup crew, and for a 20-gallon aquarium I would stick with Nassarius snails that bury in the sand and clean up meatier leftovers like leftover Mysis shrimp, along with Astrea snails that graze on microalgae and nuisance algae, plus assorted other snails.
This is what I recommend in that regard, mom:
Of course, it’s important to cycle the aquarium first before you install the cleanup crew. Otherwise the high ammonia and nitrite levels that occur during the cycling process can be deadly to your aquarium janitors. But once the aquarium has cycled, and the ammonia and nitrite levels have dropped to zero, it’s a good idea to introduce your sanitation engineers before anything else.
I prefer a cleanup crew consisting of a mixture of assorted snails at a density of no more than 1-2 janitors per gallon at the most. The snail assortment may include bumble bee snails, trocha snails, margaritas, Astrea and Cerith snails, red foot Moon snails, a fighting conch, etc., but especially Nassarius snails.
Nassarius snails are terrific detritivores and amazingly active for snails. They’ll bury themselves until they detect the scent of something edible, and then erupt from the sand and charge out to clean it up.
A varied assortment of snails is very desirable because different types of snails have different habits, seek out various microhabitats within the aquarium, and prefer to eat different things. Some are herbivores that feed on microalgae, and some of the herbivorous snails prefer to graze on it from the substrate, others like to to clean it from the rocks, and still others love to scrape algae off the aquarium glass. Furthermore, the different herbivorous snails tend to specialize on different types of microalgae and have definite preferences as to the types of algae they will eat, so it’s important to have a nice variety of snails that cover all the bases in that regard. It’s equally important to include some omnivorous snails in your assortment, which will go after meaty leftovers, along with the vegetarians. And you’ll want to have plenty of detritivores, too, which will feed on detritus and decaying organic matter in the aquarium
For best results, Astrea sp. snails should go in the tank as soon as the ammonia and nitrite levels are down to zero in order to keep nuisance algae from gaining a foothold in your tank. Introduced as soon as possible to a new aquarium, that has reached this cycling phase, Astrea snails effectively limit the development of all microalgae. In other words, they are good at eating diatoms, but will consume red slime and green algae as well.
A mixture of the snails listed above provides a good balance of herbivores, omnivores, and detritivores that are active scavengers and completely compatible with seahorses. They will clean up meatier leftovers such as frozen Mysis as well as helping to control nuisance algae.
But you must avoid predatory snails such as tulip snails, horse conchs, crown snails (Melanogena corona), and the venomous cone snails (Conus spp.), which can kill a human with a single stain from their harpoon like radula. Tulip snails, horse conchs, and crown conchs will hunt down and eat the other snails in your cleanup crew, whereas cone snails prey on small fishes in addition to presenting a deadly hazard to the aquarist.
I’m sorry to hear about the setback that you had cycling your new aquarium, mom. That’s the problem with using live fish to cycle a tank — you want a nice high ammonia spike to encourage the growth of a heavy population of beneficial pseudomonas bacteria that feed on the ammonia and convert it to nitrite, but many fish will not survive such an ammonia spike. For this reason, I prefer to use decaying cocktail shrimp or other similar biomass to provide the ammonia while an aquarium cycles. You can get a higher ammonia spike without stressing out or killing any marine fish, and you end up with a larger population of nitrifying bacteria as a result.
This is what I would recommend in your case, mom. DO NOT perform a water change or wait for the ammonia spike to go down and stabilize. Do not replace the damselfish with more sacrificial fish. Instead, add any amount of uncooked shrimp that’s about a global it to the mass of one of the damsels, and simply allow that to decompose and provide a good source of ammonia for the beneficial bacteria as the tank cycles. You can monitor the cycling process by using your test kits to observe the rise and fall in the ammonia, nitrite, and nitrate levels, as discussed below:
Cycling the Aquarium
Once you’ve rounded up the aquarium, equipment, and accessories you need, your next task is to prepare the tank for cycling. Until it has cycled, your aquarium will be unable to support life. Cycling simply means to build up a healthy population of beneficial bacteria in your tank that can carry out the nitrogen cycle and breakdown your fishes’ waste products.
Ammonia (NH3), nitrite (NO2), and nitrate (NO3) are all nitrogenous (nitrogen containing) wastes. All living aquarium animals whether they be fish or invertebrates excrete these wastes, and they are also produced by the decay of protein-containing organic matter (uneaten food, detritus, dead fish or inverts, etc.). The nitrogen cycle breaks down these wastes in a series of steps into nitrogen gas (N2) which leaves the aquarium as bubbles.
The nitrogen cycle begins with ammonia, which is highly poisonous. In the first step of the cycle, Nitrosomonas bacteria reduce ammonia to nitrite, which is also very toxic. In the second step of the nitrogen cycle, Nitrobacter bacteria convert the nitrite to nitrate, which is relatively harmless but becomes harmful when it accumulates in high enough levels. In the third and final step of the cycle, denitrifying bacteria then convert the nitrate into completely harmless N2, which of course bubbles out of the tank as nitrogen gas. In this way, thanks to the nitrogen cycle, dangerous wastes are converted into progressively less harmful compounds and finally removed from the aquarium altogether.
When we set up a new aquarium, and wait for it to cycle, we are simply allowing a big enough population of these different types of bacteria to build up in the biofilter to break down all of the wastes that will be produced when the aquarium is stocked. If we don’t wait long enough for the cycle to complete itself and the biofiltration to become fully established, and hastily add too many specimens to a new aquarium too soon, they will die from ammonia poisoning or nitrite toxicity. This is such a common mistake among us impatient aquarists, that when fish get sick and/or die from ammonia/ntrite poisoning, it is commonly called the "new tank syndrome."
When your aquarium has completely cycled, the ammonia levels will stay at zero because, now that your biofilter is fully established, there is a large enough population of aerobic (oxygen loving) nitrifying Nitrosomonas bacteria to reduce all of the ammonia to nitrite as fast as the ammonia is being produced. The nitrite levels will likewise stay at zero because there is also a large enough population of aerobic (oxygen loving) nitrifying Nitrobacter bacteria to convert all of the nitrite to nitrate as fast as the nitrite is being produced.
The nitrate levels ordinarily continue to build up, however, because there are simply not enough anaerobic (oxygen hating) denitrifying bacteria to convert all of the nitrate that’s being produced into nitrogen gas (N2). Since nitrates are being produced faster than they can be transformed to nitrogen gas, the excess nitrates accumulate steadily in your aquarium. That’s perfectly normal, since the denitrifying bacteria that carry out that final step, the conversion of nitrate (NO3) to nitrogen (N2), are anaerobes that can only exist in the absence of oxygen. For our aquariums to support life, and for the fish and invertebrates to breathe and survive, our tanks must be well aerated and well circulated so that there’s plenty of dissolved oxygen in the water at all times. That means there are normally very few areas in our aquariums where anaerobic denitrifying bacteria can survive, limiting their population accordingly (which is generally good, since some anaerobes produce deadly hydrogen sulfide gas during the decay of organic matter and would poison our tanks if allowed to proliferate).
Consequently, most aquariums lack a sufficient population of anaerobic denitrifying bacteria to complete the nitrogen cycle and convert nitrate to nitrogen as fast as the nitrates are being produced. The only way to keep the nitrates from building up to harmful levels in such setups is with regular water changes and by harvesting Caulerpa or other macroalgae periodically after it has utilized nitrates for growth. Overcrowding, overfeeding, or under filtration exacerbate the problem by resulting in more nitrates being produced and more frequent water changes being required to control the nitrate levels.
Live rock helps because the oxygen-poor interior of the rock allows anaerobic denitrifying bacteria to grow and break down nitrates. A deep live sand bed (DLSB) also helps because anaerobic denitrifying bacteria can flourish and break down nitrates at a certain depth below the sand where oxygenated water no longer penetrates, but a DLSB can sometimes be difficult to set up and manage properly if you’re inexperienced with live sand. Both live rock and deep live sand beds give aquaria denitrification ability — the ability to complete the cycle and convert nitrate to harmless nitrogen. Ordinarily, about 1-2 pounds of live rock per gallon is recommended – that amount of LR will provide your aquarium with all of the biofiltration you need, as well as significant denitrification ability. You will keep nitrates at harmless levels by performing regular water changes, harvesting Caulerpa macroalgae periodically, and good aquarium management.
Step-By-Step Instructions for Cycling a New Marine Aquarium
1) Set up the aquarium in the proper location, fill it with freshwater, and operate all of the equipment to make sure everything is working properly with no leaks.
2) Add the artificial salt mix and adjust the salinity (i.e., specific gravity) and pH of the aquarium water to the proper levels.
3) Add the substrate (e.g., live sand and/or live rock) and seed the aquarium with beneficial nitrifying bacteria.
4) Provide a source of ammonia to feed the beneficial nitrifying bacteria and encourage a large population of Nitrosomonas and Nitrobacter to develop in the aquarium.
5) Test the ammonia, nitrite, and nitrate levels regularly to monitor the cycling process and determine when the aquarium has cycled and the biological filtration is fully established.
To make everything crystal clear, we’ll go over each of these steps in more detail below.
First Step: Set up the aquarium in the proper location, fill it with freshwater, and operate all of the equipment to make sure everything is working properly with no leaks.
Prepare your aquarium for cycling by setting your system up with just freshwater at first, attaching the equipment and apparatus (filter, aeration, circulation, heater, skimmer, lighting, accessories) and testing it all for a day or so to make sure you have everything in place, and that it works correctly without any leaks or unforeseen problems.
If possible, I recommend using reverse osmosis/deionized water (RO/DI) to fill the aquarium initially and for making regular water changes once the aquarium has been established. RO/DI water obtained from a good source is ultra-pure and using it to fill the tank will help prevent nuisance algae from ever getting started in the newly established aquarium.
If you do not have an RO/DI unit of your own, you can always purchase the reverse osmosis/deinonized water (RO/DI) instead. Most well-stocked pet shops that handle marine fish sell RO/DI water as a service for their customers for between 25 and 50 cents a gallon. If your LFS does not, WalMart sell RO/DI water by the gallon for around 60 cents, and you should be able to find a Wal-Mart nearby. (Heck, even my drug store sells RO/DI water nowadays.)
However, it’s not always safe to assume that RO/DI water purchased from your LFS or your drugstore or some other convenient source is as pure as you might expect. If the merchants selling the RO/DI water are not diligent about monitoring their water quality and changing out the membranes promptly when needed, then the water they provide will not be a good quality and will not produce the desired results. I suggest that you look for an aquarium store that maintains beautiful reef systems on the premises — that’s a good sign that they know their stuff and are maintaining optimum water quality at all times, so the RO/DI water they provide should be up to snuff.
If you do not have access to a good source of reliable RO/DI water, then detoxified tap water will have to suffice for filling your new aquarium. In many areas, the municipal water supply has undesirable levels of amines, phosphates or nitrates, and in the United States, it is always chlorinated and fluoridated, so be sure to dechlorinate/detoxify the water using one of the many commercially unavailable aquarium products designed for that purpose when you add it to the aquarium.
Second Step: Add the artificial salt mix and adjust the salinity (i.e., specific gravity) and pH of the aquarium water to the proper levels.
Once assured that everything’s operating properly and there are no leaks in your aquarium system, go ahead and add the artificial salt mix and adjust the specific gravity and pH. Instant Ocean artificial salt mix is economical and works very well for seahorses. Add enough of the Instant Ocean to raise the specific gravity to between 1.022-1.025 initially.
A specific gravity of 1.024-1.025 is optimum for your most seahorses, so check it with your hydrometer and adjust the specific gravity accordingly. If it’s too low, add more of the Instant Ocean artificial salt mix to raise it up a bit. Allow sufficient time for the new salt to dissolve, and then check the specific gravity again. If the specific gravity is higher than desired, just add more freshwater to dilute it until it drops to the proper level.
Next, test the pH of the aquarium water and adjust it to anywhere between 8.0-8.4. If you used ordinary tap water to fill the aquarium, the Instant Ocean salt mix will often raise the pH to the proper level all by itself. However, if you used RO/DI water or another softened source to fill the aquarium initially, the pH will no doubt be too low at first. Water purified by such methods is very soft and must usually be buffered in order to establish the proper pH and maintain the total alkalinity and carbonate hardness of the aquarium water at the proper level.
To raise your pH to the proper range (8.0-8.4), just obtain one of the commercially made products designed to adjust the pH upwards in saltwater aquariums and use it according to the instructions. Such a product should be available from any good LFS that handles marine fishes and invertebrates; they typically include sodium bicarbonate as their primary active ingredient and are often marketed under names such as "pH Up" or something similar. If you wish, ordinary baking soda (bicarbonate) from your kitchen will work just as well for elevating the pH.
In the unlikely event that the pH of the aquarium water is too high, it can be dropped using one of the pH-lowering products from your local fish store. However, many of these products use phosphate-based chemicals to lower the pH, and this is undesirable since the phosphates can fuel the growth of nuisance algae. A better way to lower the pH is by adding RO/DI water until it comes down to the proper level.
At this point, a pH that is anywhere between 8.0-8.4 is just fine. The aquarium will cycle faster if the proper pH is maintained, but we won’t worry about fine-tuning the pH until after the aquarium has completely cycled. In fact, once you have adjusted the aquarium pH between this range initially, you don’t need to check it again until after the cycling process is complete and the biological filtration is fully established.
After you have adjusted the salinity and pH of the aquarium water to the proper levels, leave everything running continuously for at least a few days, allowing the various components and water to "settle in" before adding your microbes and "seeding" the tank with beneficial bacteria that will eventually establish your biofilter. This will make sure that the specific gravity and pH have stabilized and that the aquarium equipment is operating properly before you proceed.
Third Step: Add the substrate (e.g., live sand and/or live rock) and seed the aquarium with beneficial nitrifying bacteria.
Now that the pH and specific gravity of the aquarium water are at the proper levels, and the tank has had time to settle in, you can go ahead and add the substrate and seed bacteria. If you are using either live rock or live sand, as I recommend, it will contain all the bacteria needed to seed the tank. I suggest a thin layer of live aragonite sand no deeper than an inch or so.
Once the sand substrate is in place, you can add the live rock and position it in attractive arrangements. Ledges, overhangs, and caves will offer shelter and interest to your aquascaping, but be careful to make sure that the live rock is anchored securely in place so that there is no danger of collapses or the rock shifting unexpectedly.
If you have artificial decorations such as synthetic plants or fake corals, and they can also be added to the aquarium at this time.
If you are not using live rock or live sand, you can seed the aquarium with nitrifying bacteria by adding a live culture product such as marine BioSpira to help kickstart the cycling process instead. Or, as an alternative, some hobbyists will simply add a handful of gravel or filter media from an already established marine aquarium to seed a new tank with beneficial bacteria, but if this is done, you must be sure to harvest the material you use for seeding from an aquarium you know to be healthy. You don’t want to risk introducing pathogens or parasites to your new aquarium by adding seed material from a tank that has lost fish or had disease problems of any kind. (Do NOT bring home filter material or sand or gravel from an aquarium at your local fish store to provide seed bacteria!)
Fourth Step: Provide a source of ammonia to feed the beneficial nitrifying bacteria and encourage a large population of Nitrosomonas and Nitrobacter to develop in the aquarium.
Once the aquarium has been seeded with beneficial nitrifying bacteria, it is necessary to feed that bacteria with ammonia so that the population of good bacteria can grow and thrive. There are a number of different ways to 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.
And there is always the possibility that the damsels or mollies could be carrying disease, and it would be a shame to introduce pathogens or parasites into a new aquarium by using such expendable fish to cycle the tank. The damsels or mollies are likely to be stressed by the high ammonia and nitrite levels during the cycling process, which leaves them susceptible to disease, and we don’t want to put our seahorses at risk simply because of the way we cycled their aquarium.
So all things considered, I suggest you try 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. Depending on the size of the aquarium, I like to use a piece or two of cocktail shrimp (regular uncooked eating shrimp from the grocery store) and leave this in the tank to decay during the whole cycle. The decaying shrimp produces plenty of ammonia to fuel the cycling process.
IMPORTANT: do not operate your protein skimmer, ultraviolet sterilizer, or ozonizer, or make water changes while your new aquarium is cycling. Remove chemical filtration media while the aquarium is cycling and avoid adding any ammonia-removing liquids or ammonia-sequestering products (such as BIO-Safe, Amquel, Ammo-lock, Aqua-Safe, etc.) while the tank cycles. You want a nice high ammonia spike, followed by a nice high nitrite spike, when the aquarium cycles in order to build up the largest possible population of the nitrifying bacteria that feed on ammonia and nitrite, so using any type of filtration or additives that could reduce the amount of ammonia or nitrite at this time will actually hinder the cycling process and be very counterproductive.
Fifth Step: Test the ammonia, nitrite, and nitrate levels regularly to monitor the cycling process and determine when the aquarium has cycled and the biological filtration is fully established.
Now that you have seeded the new aquarium with beneficial bacteria and provided a source of ammonia to feed that bacteria, all you need to do is to wait for a sufficient population of the desirable bacteria to build up in the aquarium. By using your test kits for ammonia and nitrite regularly (daily) at this time, you can monitor the cycling process and keep track of how everything is progressing.
For example, about 3 days after you add the cocktail shrimp (or expendable fish, if you go that route), you should 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 to monitor the progress of the process. As described above, 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.
At this point, you can doublecheck the specific gravity and pH of the aquarium, adjusting them if necessary to make sure they remain at the desired level. It is now safe to add your chemical filtration media, and you can begin stocking the aquarium by adding live macroalgae and your cleanup crew of sanitation engineers.
To be extra safe, many hobbyists like to wait an additional six weeks after introducing the macroalgae and cleanup crew before they acclimate the first seahorses to their new systems. This gives the new aquarium a chance to further break in and stabilize, and also serves as a quarantine period for the aquarium janitors and live plants. Any parasites they may possibly have been carrying that could pose a risk to the seahorses would require a vertebrate host in order to survive, and after six weeks without any fish in the aquarium, any such parasites should have been eliminated and are no longer a cause for concern.
Best of luck cycling your new seahorse tank, mom, and finding a nice selection of snails to serve as your sanitation engineers.