Cleaning the fish tank is never fun. Ask any tropical fish hobbyist with a pair of angelfish, some gravel and a few plastic plants.

But what if the tank is 35 feet deep and has a window the size of a drive-in movie screen?

In what may be the mother of all fish tank spring-cleaning projects, the Monterey Bay Aquarium is putting the final touches on the overhaul of its Outer Bay tank — a 1 million gallon structure that holds more water than the other 90 tanks in the aquarium combined and ranks among the largest tanks in the United States. It’s all part of a $19 million transformation that re-opens to the public Saturday.

“It’s been like remodeling a 30,000-square-foot home while 18 people are living in it,” said David Cripe, special exhibits coordinator at the aquarium. “We stressed over how we were going to move things and catch things. But we got it done two weeks ahead of schedule.”

The exhibit, re-christened The Open Sea, features new species in the big tank and other nearby displays, including a sand bar shark from Oahu, tufted puffins and other seabirds, a high-tech interactive video wall display on plankton, deep sea jellies and numerous art installations. Aquarium scientists also plan to bring in a new juvenile great white shark in September, the sixth white shark the aquarium will have put on display since 2004.

No aquarium in the world currently has a great white shark on display.

A difficult journey

On Monday, dozens of volunteer docents getting their first look stepped around painters, welders and other construction workers who were putting the final touches on the exhibit. As they oohed and aahed at the refurbished marquee tank, with shimmering schools of sardines darting past languidly floating mahi mahi and hypnotic sea turtles, they may not have realized the long road of scientific trial and error, setbacks and elbow grease to get the project this far.

The aquarium closed the big tank to the public last August. It seemed that the bluefin and yellowfin tuna — some of which had grown to more than 300 pounds from their original sizes of as small as 25 pounds — were creating such turbulence in the water as they swam fast that glass tiles on the inside of the tank were falling off.

“The green sea turtles were eating the tiles,” aquarium spokesman Ken Peterson said. “They didn’t get hurt. They’d pass them. But we didn’t want to risk it.”

The tank needed an upgrade anyway, aquarium managers thought. So they drained all the water into the ocean. But not before catching the roughly 10,000 specimens in the tank first. That took three weeks.

Aquarium biologists used a specially designed net to catch the 9,000 sardines. They caught the three dozen tuna with fishing line and barbless hooks. They lured the sea turtles and hammerhead sharks with food and lifted them with gurney-like slings out of the water.

Some animals didn’t make it. A few tuna were too big to move and had to be euthanized, Cripe said. One hammerhead shark also died. But the vast majority survived the upgrade. They were placed in tanks on trucks and shipped to an aquarium facility 10 miles north in Marina.

Workers under the direction of contractor Rudolph and Sletten in Redwood City, which helped install the tank when it was first constructed in 1996, stripped off the tiles. They coated the fiberglass walls with new sealant. They installed a wave machine to create chop on the water’s surface, like in the open ocean. They polished the massive acrylic windows and added new water-heating systems — even a “turtle elevator” to make it easier for veterinarians to lift sea turtles from an adjacent holding pen to the main tank. New lighting makes the colors of the animals in the tank shimmer as they pass in front of the yawning window.

Where once visitors saw sides and a bottom, now they see what appears to be endless blue. It’s the same sight that many of the species see as they are migrating up to 10,000 miles each year across the Pacific Ocean, a pattern that the new exhibit highlights, based on research with satellite tags done in the past decade by Stanford University, UC Santa Cruz and other marine centers.

“It feels more like you are seeing the open ocean now,” said Jaci Tomulonis, senior exhibit developer. “Before, it was like an exhibit tank.”

Conservation education

Additional exhibits explaining creatures like the humpback whale, leatherback sea turtle and albatross are scheduled to open in February. And they, like the refurbished wing opening on Saturday, carry conservation messages to the aquarium’s 1.9 million annual visitors about overfishing, plastic pollution in the ocean and global warming, part of a trend the aquarium has highlighted increasingly since it opened in 1984 with a $55 million gift from tech titans David and Lucile Packard.

The aquarium is even the chief sponsor of a bill moving forward in the California Legislature to ban the trade in shark fins, a subject that has split the Chinese-American community and caused considerable political outcry.

“It’s not enough to show people beautiful ocean animals, particularly when we know the threats they face,” said Peterson. “We’re worried. We want people to engage and make a difference.”

Contact Paul Rogers at 408-920-5045.