In the spring of 1998 a story was carried by Associated Press that received wide play in newspapers and on television concerning the latest pet fad in Japan — the keeping of jellyfish, especially by single Japanese women. I am not sure how widespread this fad actually is in Japan, but when I was there in January, I visited a number of pet shops and saw only one small jellyfish tank on display, and only one other store had a single jellyfish specimen for sale. According to the story, the hypnotic swimming movements of the jellyfish were felt to have a calming effect on their owners.

One quote in the story stated that they were easy to keep and could be left alone for a week without needing to be fed, making them the "perfect pet." Unfortunately, nothing could be further from the truth. It is very unlikely that these animals live more than a few short months in these "home systems" now being sold in Japan. What is even more unfortunate — for a number of reasons — is that, perhaps due to that story, we are now seeing jellies appearing in pet shops and wholesalers here in North America.

Sea jellies, of which there are thousands of species in temperate and tropical waters, have many special requirements — some of which are known, many of which are not. This includes such things as water movement, the effects of animal population density on growth, the effects of photoperiod, food (types, sizes, frequency of feeding and amounts are all variables that need to be investigated), the role of temperature fluctuations in reproduction, their natural life spans (many species live less than a year) and the role of trace elements.

Some jellyfish, such as Cassiopea and Mastigias species, contain symbiotic algae and require high light levels of the proper spectrum, just as live corals do. Most jellyfish also require frequent feedings of live food, so culturing systems for brine shrimp, rotifers and other microscopic foods must be constantly maintained.

Keeping jellyfish is not as simple as the story noted above made it appear, and they are certainly not for beginners. As with so much of the aquatic life kept in aquariums today, some species of jellies can grow quite large and require larger systems as they grow. Growth is often rapid, especially in species with life spans under two years, and system designs need to take this into account. As with any organism we keep in captivity, we should strive to do so for the length of its natural life span. Keeping jellies alive for a few months does not mesh with this goal, and I would urge people not to succumb to the urge to purchase these animals unless they have access to the necessary expertise, funds, time and energy required to keep the few available species alive and well in captivity.

At present, only public aquariums have had the resources to properly display and breed some species of jellyfish, but I expect in the future dedicated advanced hobbyists will be able to keep some of the smaller, more easily maintained species. Some, such as Aurelia aurelia, breed quite readily in captivity, and sustainable populations could be maintained in aquaculture facilities for the pet trade. But until the costs for the systems necessary to maintain and feed these animals properly comes down, they will limited to individuals and/or institutions with the financial resources and dedication required. For now, admire these animals at your local public aquarium or on video, and do not succumb to the temptation to purchase and keep them in 20-gallon "jelly tanks."

Other Than RO Water
Q. I have heard so much about using reverse osmosis (RO) water in reef tanks, but I can't afford an expensive RO unit. I was wondering if I could use dehumidifier water as a cheap substitute. I know it has no minerals in it, but supplements take care of that for me. What advantages does RO water have over regular tap or dehumidifier water?

A. I once wondered the same thing as I sat in my basement and saw the amount of water my dehumidifier would collect in the summer months. After thinking about it for some time I came to the conclusion that using this water in my reef tank may not be such a good idea, and I'll tell you why.

In the summer months you usually get a lot more water being produced than in the drier winter months. Conversely, your aquarium probably has a greater evaporation rate in the winter than in the summer. Therefore, depending on the evaporation rate of the aquarium and the amount of humidity in the air, you may or may not be able to generate enough water to meet the demand. This, of course, varies depending on where you live and where the aquarium is located in your home.

I was also unsure as to what the coils in the dehumidifier were made of. It might be possible that water forming on the coils could pick up trace amounts of aluminum, zinc or copper. And, as the water condenses it could absorb compounds from the surrounding air, such as nicotine from cigarette smoke, compounds from household cleaning products and so on.

The final thing that made me choose against using this water was the color of the plastic container the water collected in — it gradually became a rusty orange color! I decided that the money and time I had invested in my reef tank was not worth risking on a questionable water source.

Reverse osmosis units can be purchased for under $200 and may cost as little as a good dehumidifier. So why take the risk? If you are really intent on trying this, I would suggest having the water checked for organic compounds and metals, but the cost of having these tests done will most likely be greater than buying an RO unit. I would also purchase a deionizing column and pump the dehumidifier water through it first to remove any possible contaminants before using it.

RO units have several advantages over tap water and dehumidifier water. The water comes from the tap, which is usually safe and is filtered by a fine sediment filter and carbon block before it enters the RO chamber. Once it passes through the membrane, many units also pass the water through one or more deionizing units. This results in very pure water that is low in organics, dissolved minerals and nutrient compounds. If you live in an area with tap water that is very low in phosphate and nitrate and high in calcium and magnesium, you may be able to use this water directly. However, most city water treatment plants regularly add phosphate to the water under federal guidelines, so it is usually safe to assume that your tap water will contain phosphate.

Down South
Q. I'm planning to install a marine aquarium with fish and invertebrates (hard and soft corals, sponges and so on). I have a 150-gallon aquarium (24 x 22 x 72 inches) with the following equipment:

Amiracle Berlin filter (model BFL), capacity of 300 gallons, with a Little Giant 3MDQX-SC pump; Magnum 350 canister filter; 15-watt ultraviolet sterilizer; Aquanetics 1/6-horsepower drop-in type chiller unit; six powerheads with wave motion timer; four very high output fluorescent lamps (two actinic, two daylight) with a timer.

Is this enough to run a reef aquarium? Do I need any other piece of equipment? I know there are a lot of factors to consider, like pH, nitrate, nitrite, ammonia, salinity, temperature and so on, but right now the important concern is the equipment. I'd appreciate your kind response as I really need your help. Thanks in advance!

A. Thank you for your letter! As far as your system design goes, I have a few suggestions. I would highly recommend you purchase a protein skimmer unless this is already included in the Amiracle Berlin filter. I would also not use bioballs or any other biomedia in the filter. You won't need the ultraviolet unit unless there is a disease outbreak, and most likely it is not strong enough to do much good anyway. I would not install it unless you run into disease problems.

Your chiller may be undersized. In your climate you may need a 1/4-horsepower unit at the least, maybe even a 1/2-horsepower model. You need to consult with the manufacturer and tell them what the average temperature is in the room you want to keep the tank in and at what temperature you want to keep the tank. They can then calculate what size chiller you need. It is much better to have excess capacity than inadequate capacity when it comes to chillers. An undersize chiller will run constantly and wear out quickly. Everything else looks fine!