How to Repair Glass Aquarium Leaks

Fish Tank

A leaky aquarium is one of the most annoying things an aquarist may experience. It normally begins with a drop or two of water hanging over the tank's bottom edge, which quickly evolves into a drip...drip...drip, at which time you grab a bunch of paper towels and begin sopping up the water while trying to find out where the leak is coming from.

How Aquariums Are Constructed

Understanding how glass aquariums are made will assist you in determining the source of the leak. The structural integrity (what stops it from coming apart) and water tight integrity of a glass aquarium are established when the glass meets the glass. When you look at where the glass panels meet, that minuscule fraction of an inch between them where the silicone resides is where the rubber meets the road. The silicone that is spread out within the tank where the glass panels meet improves water tightness and strength just little. The tank will contain water without leaking if it is built properly and the silicone between the glass panel edges is faultless, with no bubbles or cracks in the silicone.

Find the Leak

Finding the source of the leak might be tricky. It doesn't appear to be where you see the water on the outside of the tank nine times out of ten. You may see the silicone sealant separating or curling up from the glass within the tank if the tank is old, wasn't built properly, or hasn't been cleaned properly over time. If the silicone sealant in the tank has evident damage, it would be an excellent location to start looking for the source of the leak.

Search the Seams

A little jet of water can sometimes be seen blasting out of a silicone gap in the glass. There is a simple approach to determine the source of the leak if there is no evident damage to the silicone behind the water stream. Colored water is poured into a syringe (food coloring or ink works well). Slowly depress the syringe plunger after inserting the syringe needle into the silicone where the water is flowing out. You'll be able to watch the colored water enter the silicone and follow the "tunnel" that the tank water used to return to its source.

Keep in mind that all aquarium leaks originate from within the tank. You might be able to block the leak where it starts by smearing silicone on the outside of the tank where the water is leaking. Also, keep in mind that water can travel a significant distance between the silicone and the glass in the tank seams before it reaches the outside.

Repair Techniques

Unless you prefer to just smear some silicone on the outside of the tank where the leaking water is visible, you will have to empty the water down to below where the leak begins in order to repair it. You may also try to block the leak with a strip of duct tape. We've found that none of these remedies works for very long, if at all. The fundamental reason for resealing the tank from the inside rather than the outside is that the inside patch is pressed into the glass by the water pressure, whereas the outside patch is pushed away from the glass by the water pressure.

Start emptying the tank 1 inch at a time with a siphon hose. Keep an eye on where the water appears on the exterior of the tank and cease draining it when it stops leaking. Keep an eye on the water level in the tank for signs of damage to the silicone, such as loose silicone or other silicone damage. Mark the damage location on the outside of the tank using the felt tip marker. If you've discovered that the leak is coming from the bottom of the tank, empty it completely and discard the substrate. It may seem like a lot of bother to go to, but you'll discover that it's easier in the end than fighting the water and substrate that are polluting the repair site.

At this point, you will probably want to move the fish and other critters in the tank to a temporary tank.

What You'll Need

  • 100% Silicone Sealant without any additives such as mildew control.
  • Acetone for cleaning the glass surface areas and your hands, later.
  • Single Edged Razor Blades preferable in a holding tool.
  • Paper Towels for cleanup and soaking up water.
  • Felt Tip Marker for marking where the leak is appearing.
  • Replacement Water to refill the tank when it is patched.


Scrape Away Old Silicone

To begin the repair, carefully cut the silicone 1" around the source of the leak using the single edge razor blade. Scrape off all of the silicone from the glass, being careful not to let the blade slide between the panes. Allow to dry after cleaning the scraped area with an acetone-soaked paper towel.

Apply New Silicone

When the repair location is completely dry, reopen the silicone tube and apply the silicone to the area, covering the old silicone on both sides of the leak. With a piece of paper (a business card works well) or a flexible piece of plastic, smooth the silicone down and out. Don't just throw silicone on the task because you assume a lot of it will suffice. It not only looks bad, but it also doesn't produce a decent seal.

Let Dry and Refill

Allow the to cure for 24 hours after putting and smoothing it into position, then refill the tank with freshwater (no point wasting if the patch doesn't work) and check for leaks. Allow the tank to sit for 24 hours to ensure that it isn't leaking again, then empty and reassemble it as if it were a new tank.

If your repair didn't work you may have to strip the tank and Major Aquarium Repair.