He covered the tanks' tiled surfaces with rocks, as well as reconfiguring each of the tanks' pipes to reduce energy usage. The Zoological Society added a classroom next to the fort, and it installed a tank underneath the fort to store saltwater. The organization also repainted the interior for the first time in Castle Garden's history. These modifications cost over $30,000. The fort's design continued to pose issues; for example, aquarium officials discovered in 1905 that the roof skylights were causing some of the fish to become blind. The Zoological Society installed new pipes at Castle Garden in 1908. Meanwhile, by the early 20th century, city officials were planning to rebuild Battery Park, and they considered replacing Castle Garden with a skyscraper. By January 1911, officials instead planned to expand Castle Garden, adding semicircular wings to the west and east for over $1 million. Each wing was to contain three tiers of tanks and classroom space. The Zoological Society asked the Board of Estimate to allocate $1.75 million to the renovation, but the board still had not funded the renovation of Castle Garden by 1916. Townsend said the aquarium's mechanical facilities needed major upgrades; according to Townsend, the mechanical equipment under the fort was flooded at high tide, and power was provided by coal bunkers, which had to be manually replenished every four days. In addition, the fort had never been properly renovated for the aquarium's use, and the second story's wooden frame was flammable. Townsend said the annexes would not only provide additional exhibition space but also allow the mechanical facilities to be upgraded. In 1921, Townsend announced that the Zoological Society would spend $75,000 to construct an electric plant in the basement, replacing a steam plant on the south side of the fort, and then install two tanks in the space formerly occupied by the steam plant. This work was funded by a bequest from Mrs. Russell Sage. The same year, a bust of Jenny Lind was dedicated and installed at the center of the fort. The Board of Estimate voted in December 1921 to provide $105,000 for the construction of an additional story atop the fort. By early 1923, the Zoological Society was carrying out the renovations at a cost of $86,000. In June 1923, the board voted to give $76,500 for the construction of an additional story above the fort. The Zoological Society planned to add