The hi-tech system cost about HK$500,000 to install. Artificial lighting – crucial for photosynthesis by microscopic algae living within coral polyps – is set to a timer that imitates diurnal rhythms, and the carefully calibrated saltwater is circulated to bring a constant flow of nutrients to the corals.

Palla’s aquarium adventures began when he bought a tank for his niece’s goldfish. Before long, they had moved on to bigger tanks and from freshwater fish to marine species.

Keeping aquariums is a popular hobby in Hong Kong. Freshwater systems are the most common as they are simple to set up, and suppliers estimate that such enthusiasts outnumber people with saltwater tanks two to one. However, the popularity of marine aquariums spiked in the wake of Disney’s 2003 hit animated feature, Finding Nemo, and more sophisticated tools now help make it easier to manage them.

Sensors in Palla’s tanks are linked to the internet so that he can monitor conditions while travelling abroad and make adjustments accordingly.

“They control everything, like salinity, temperature and oxidation-reduction potential. If something goes wrong, I get an email and I can check the [condition[. I don’t let my maids handle them as [managing saltwater aquariums] is quite technical,” he says.

Keeping live coral proved to be quite a challenge and they grasped the techniques after much trial and error, says Palla’s wife, Stephanie Hui.

“When we first kept corals, they all died. We put the struggling ones into the sea in the hope that they might recover in the real marine environment.”

But the family now has professional help from Homi Aqua, an aquarium installation and maintenance service; the owner, Homi Chan Hoi-ming, makes weekly visits to tend to the corals.

It is difficult to get coral established in a tank environment, Chan says.

“Live” rock – usually coral skeleton covered with bacteria and other organisms – is used as a biological filter to digest ammonia that is toxic to fish and convert it to other nutrients. But the imported rock suffers wear and tear during shipment, so water quality is quite bad at first, Chan says.

It takes at least one month for the water to improve sufficiently so hardier fish and coral can be introduced, and between six months and a year to fully establish a marine aquarium.

Coral sold in Hong Kong come mainly from Southeast Asia and Australia, and novices usually start with soft coral, which has lower demands on light and water quality, before progressing to hard coral.

Prices for corals range from HK$100 a piece to more than HK$10,000, but Chan says they are generally cheaper than fish, some of which may cost upwards of HK$100,000.

Swimming instructor Yu Ho-chi, however, confines the inhabitants in his aquarium to tropical fish. His collection includes Australian scribbled angelfish and emperor angelfish from Maldives, but most prized is a clarion angelfish, which he bought for HK$9,000.

Their maintenance adds up to a tidy sum. It cost HK$100,000 just to set up his aquarium and air-conditioned quarantine tank, and electricity charges and fish feed set him back by more than HK$3,000 each month.

Yu doesn’t mind the expense, though. The hobby gives him plenty of pleasure and helps develop his patience.

“I don’t watch television and just enjoy looking at my fish and taking care of them,” Yu says.

But it is painstaking work: water in the tanks has to be changed weekly – a slow, four-hour process – and he must keep a keen eye out for signs of illness in the fish, little white spots appearing on their skin or bored expressions. Sick fish have to be quarantined and treated immediately, he says.

One of the more unusual aquarium collections in town belong to The Ocean, a seafood restaurant in Repulse Bay. Besides an enormous tank brimming with colourful reef fish and coral in the main dining area, its private room holds a couple of two-metre tall aquariums with colonies of graceful jellyfish.

The job of looking after the translucent, umbrella-shaped creatures fall to Sun Yu Wun-sun and his brother Keith Yu Wun-kei, owners of an aquarium installation business in Tsuen Wan called Jari.

Keeping healthy jellyfish is no easy task, says Sun, who worked in Ocean Park for five years before setting up the company in 2012.

“Each species requires a different [water] temperature. And they need to have enough food [brine shrimp and sea snails, for instance]; otherwise, the jellyfish will start to shrink,” he says, recalling how the restaurant’s bigger jellyfish began to waste away in the first months of its opening.

About a third of the water has to be replaced each week, and the brothers clean the tanks at The Ocean before checking on the support system that generates a circular flow of water to simulate ocean currents.

(Although jellyfish can propel themselves around by squirting water through their mouth, without flowing water they tend to sink to the bottom of tanks or stick to the sides).

Sun kept pet fish as a teenager and, after failing his Form Five exams, got a job in Mong Kok’s “goldfish market” (Tung Choi Street North), where he learned to breed marine as well as freshwater fish, before joining Ocean Park.

“They don’t usually employ people without basic academic credentials but hired me eventually because of my sincerity,” he says.

Assigned to the jellyfish aquarium, he started doing menial cleaning and rose through the ranks to source and breed jellyfish.

Sun was later dispatched to Japan to learn about keeping jellyfish. By the time he left Ocean Park, he had become so well respected he was invited to serve as consultant to jellyfish aquariums in China, the Philippines and Taiwan.

Hongkongers began keeping jellyfish as a hobby in 2000 but the opening of the jellyfish aquarium in Ocean Park in 2006 further piqued interest, says Keith, a former marketing professional.

But many people couldn’t keep their jellyfish alive because their aquariums were not properly set up.

In the past, the brothers used regular glass tanks, which they retrofitted, adjusting filtration systems so that the delicate jellyfish would not be sucked up and mangled.

But later Jari began creating their own specially designed jellyfish tanks, with manufacturing done in Chinese factories.

To Cedric Jacob, The Ocean general manager, the display of marine life in his restaurant reflects its theme.

“We serve sustainable seafood ... [and support] the idea of taking care of the ocean. We grow corals. We take care of our fish. Customers are amazed by the [marine] animals. Humans are attracted by water.”

After all, flowing water in feng shui signifies more business and money coming in, he adds.