Aquatics Unlimited: Articles: Fixing a Big Aquarium Leak
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Fixing a Big Aquarium Leak

for the week of 8/27/98

Tank SealIn larger aquariums, or smaller aquariums with major leaks, simply slapping a patch of silicone over the affected area may not be adequate. Often, such aquariums hold water for a few weeks or months, then burst the seam - sometimes with greater water loss than before.

The reason for this is that there is actually a double seal in aquarium construction. First, there is a structural bead of sealant between the two bonded pieces of glass that actually holds the aquarium together. The second bead of silicone, that was discussed in Fixing a Small Aquarium Leak, adds a little strength, but primarily prevents leaks by plugging small gaps in the structural seal. In cases of major leaks, a large portion of the structural seam may have come apart, leaving a huge gap between to two sheets of glass. Replacing the secondary seal may temporarily stop the leak, but eventually, water pressure stretches the new seam until it lets loose.

Large aquariums with major leaks should ideally be disassembled, starting by carefully removing the bottom framesby slicing the sealant under it with a razor cutter or hobby knife. Then, the bottom glass shoul be removed. A razor knife will work for thin-glass aquariums, but piano wire (or a thin guitar string) may work better on thicker glass. Generally, only the bottom need be removed, but if a side seal is affected, you may need to disconnect all five pieces of glass from one another.

The glass pieces should be thoroughly cleaned and dried. Then a bead of aquarium-safe silicone sealant should be applied to the edges of the side glasses. Unlike the secondary seal, which should be pushed into place, this bead should be applied like toothpaste, with the tube pulled along the edge. The bottom glass can then be carefully lowered into place, and the seal allowed to cure. After curing, excess sealant should be removed from both inside and outside, and a new inner seal applied as in Fixing a Small Aquarium Leak, and the frame glued back into place with silicone.

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