Kelp Forest Tank Under Construction: Repairs Underway

From January 6 through February 7, 2014, Birch Aquarium’s kelp forest exhibit will be off display while minor repairs are made to the tank’s concrete structure. Our aquarists will also use this opportunity to freshen the exhibit’s look with new animals. We are grateful for your support so that when the exhibit reopens on February 8 [subject to change], visitors will enjoy an even better representation of Southern California’s kelp forests. Our popular kelp tank dive shows and web cam feeds will also resume at this time.

This is the second of three articles describing the construction project and its developments. Post #1: Getting Ready

In early January, Birch Aquarium’s kelp forest tank was drained to begin repairing areas of rusted rebar in the tank’s back wall. With a two inch-diameter drain hole regularly used to clean the tank, aquarists drained the 70,000-gallon tank. The water level inched down the tank’s 12-foot high acrylic window, taking a day to completely drain.

Kelp Tank Repair 2014

The window’s manufacturers were also onsite to monitor and learn from the draining process. Brad McKee, a structural engineer from Reynolds Polymer Technology, traveled from Colorado to La Jolla to study how the tank’s 10-inch thick acrylic responded to the release of water pressure. In aquariums, acrylic is valued for its clarity, strength, and elasticity. Because acrylic is plastic (not glass), a large aquarium window such as the one in the kelp tank will flex as the weight of water is removed. This deflection, as engineers call it, is predictable and not permanent. Measuring with carefully positioned dial instruments every 15 to 30 minutes, Brad found that many areas of the kelp forest window experienced deflection of one quarter to half an inch—very close to what was predicted.

In order to reach the draining stage of the project, aquarium staff planned for months to get everything ready. An important final step in this preparation was the removing of the tank’s seaweed collection and its 200 animals (30 species) to other display tanks and/or off-exhibit temporary housing. For example, some seaweeds were moved to Tide Pool Plaza and a few fishes (such as the guitarfish, yellowfin croaker, and others) were moved to ElasmoBeach. In January 2014, Birch Aquarium’s husbandry staff moved the remaining giant kelp and animals. First, aquarists moved seaweeds and smaller fishes using hand-held nets. Then, the large fishes, including leopard sharks and a 200-pound giant sea bass, were moved. Having worked with these fishes for years during feedings, dive shows, and while performing tank maintenance, our aquarists have an in-depth understanding of the animals’ behavior that ensured the entire process would run smoothly.


Outside the tank, contractors from Hamilton Pacific, Inc. are repairing corrosion in the kelp forest tank’s rear wall. The process began by drilling into the concrete six inches and injecting a high-pressure epoxy to fill the tank’s cracks. Zinc anodes, which prevent corrosion by drawing stray electrical current away from wall-supporting rebar, are inserted into holes near the epoxy (see photo). Anodes and rebar are then connected by external wires. Handfuls of concrete slurry are massaged into the holes to cover the zinc anodes.


In early February, the kelp forest tank will be refilled with seawater pumped to Birch Aquarium via Scripps Pier. Birch Aquarium’s husbandry staff will again be on hand to watch the seawater crawl back up the glass, a few inches at a time. Once the tank is refilled and the animals are returned, the kelp forest exhibit will reopen to the public, representing the diversity found in the kelp forest off La Jolla’s coast even better than before.

In our next blog post, we wrap up the construction project and get ready to reopen the exhibit.

Kate Jirik

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  • K.L. Parry
    January 31, 2014 at 6:39 am

    I was there years ago and was fascinated with all the Jellyfish Tanks. They were beautiful – thank you! I look forward to when I can return 🙂
    K.L. Parry

  • Kevin
    February 8, 2014 at 12:05 pm

    How do you get the really big fish out? Some sort of sling maybe, and a couple people who don’t mind getting a little wet and/or fishy?

    • h6johnson
      February 10, 2014 at 6:53 pm

      Hi Kevin, yes, divers (aquarists) helped remove the fish from the tank. We didn’t use a sling, but we did have a crane and large plastic tubs to remove the largest fish.

  • Susan Moynihan
    February 9, 2014 at 6:52 am

    Is the kelp tank back open? Hope all went smoothly with the repairs. Did you get an exact time for the draining? My students are dying to know, thanks!

    • h6johnson
      February 10, 2014 at 6:53 pm

      Hi Susan: yes the tank is back up! We should be able to email you tomorrow (Tuesday) with the time it took to drain the tank. Thanks!

    Scripps Institution of Oceanography UC San Diego