Fix that leaky tank.

Tank sprung a leak? Saw one in the neighbors garage,said you could have it free cause it leaks?Its not difficult to reseal a leaker,if you have time and some basic skills with tools. Is it worth it to you though? Me personally I enjoy time spent working on my hobby and love to get free tanks. So I have repaired many tanks over the years from 2.5g up to 125g.

For cost consideration,you’ll need:

  • a tube of aquarium safe silicone
  • caulking gun single edge razor blades
  • Latex gloves
  • scotchbrite pad or fine steel wool
  • rubbing alcohol
  • paper towel
  • Optional:
    • wood chisel
    • shop vac
    • masking tape

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If you have some or all of that laying around then great! Whatever you do have to buy figure if buying those items is more than you want to spend on the project. Then consider if you really want to invest the time in doing it. Is a couple hours too big a bite out of your life to devote to solving a problem you could easily fix with a few bucks and a quick trip to the local fish store?

You’re still reading! So if you’re cheap and have a limited social agenda like me lets fix this leaker! How do you locate the leak? You don’t. Silicone sticks best and most permanently to clean glass. It will stick to cured silicone but not well and usually not permanently. So we are going to reseal the whole thing.

The first and most important step is to get the glass clean. I cant emphasize this enough, the whole project hinges on getting the glass clean so the silicone can stick. For the majority of leaky tanks there is no need to take the tank apart, just removing and replacing the silicone inside the tank will do the job. So starting with a clean, dry tank you need to scrape out the silicone.

I usually start with a freshly sharpened wood chisel. This will remove the bulk of the silicone much more quickly than a razor blade. Work down the sides and along the bottom and remove all of silicone you can. Shake out or vacuum out the bits. Now go back in and scrape those seams again now with the razor blades. Keep scraping till you are 100% sure you have the glass perfectly clean. Then scrape it again. Shake or vac it out again. Now take your scotchbrite or steel wool and go over the seams rubbing where you removed the silicone. This will remove some of what you missed but even better bits of the scrub pad will stick to any thin skin of silicone that remain on the glass, making removal a simple matter of scraping off the discolored areas with the razor blade. Some have reported the scotchbrite will scratch the glass. I haven’t seen this. Still, just rub it over the areas that will be covered with silicone. Repeat this last step if you think necessary, I usually do. Remember the part about needing the glass perfectly clean? Vac or shake out the bits again.

Now you are going to clean the glass with the alcohol. Wet a paper towel and rub down all the areas to be resealed .Let air dry. Finally we get to the part where we reseal the tank! This last part you really want to do outdoors or in an open garage. Curing silicone releases acetic acid. Very irritating to breathe,really not good for you. So don’t do it in the house. Now the next step I’m including is something I’ve never done. To get a really clean look you could use masking tape and mask next to the area you are sealing. Leaving room for a 1/4″ to 1/2″ bead depending on how big the tank is. If you do this you must remove the tape IMMEDIATELY after applying the silicone.

Let it sit a little while and you’ll pull the seal out when you remove it. Let it dry and you’ll glue all that tape into your tank. Working with the silicone I always wear latex gloves. You will get some on you. And it will not wash off or scrub off. It will dry on you and you’ll spend days rubbing and peeling it off. The cheap gloves they sell in the paint department are fine.

Now for the silicone. At some hardware or fish stores you will be able to find silicone tubes clearly marked “safe for aquarium use” I have not, or occasionally located a dusty old tube for 4x the price I’m willing to pay. I have had great results using GE type 1 window and door. It clearly says on the tube “not for aquarium use”. I have resealed dozens of tanks with it and built many in tank structures with it. Worked great and doesn’t bother the fish. What I make sure I DON’T see on the tube are the words “mildew resistant” “kitchen and bath” or “Bio-seal”. Mildew resistant silicone contains poison and WILL kill your fish!

If you’ve caulked a window or tub the next step is easy. Put the gloves on. I cut the tip off the silicone tube at a 45 degree angle far enough back to lay down a bead the size I want. Smaller tanks 1/4″ bead big tanks 1/2″. Using the caulking gun Ill lay down a bead all the way around the bottom. Start in a corner,go across to the next corner. Do it in one sweep if possible. Smaller tanks you can do standing in one spot. Bigger tanks you’ll have to move around so you can reach comfortably. Don’t try to do it from an awkward position or you run the risk of messing it up. After you got the bottom done do the sides. Go from the bottom to the top laying down the seam in one motion. Now the tank is all sealed up! Next you are going to smooth out the bead with your finger. Same as before go around the bottom then up the sides. You want to push the silicone into the corners and smooth it out. This serves the dual purpose of filling any gaps, and making it look smooth. If there is excess wipe it off your glove with a paper towel. When it looks nice and neat you are done. If you taped it, peel the tape off now.

Here is another useful tip I haven’t tried yet. If you have silicone left in the tube lay out a few beads on a paper towel about the same as the beads in the tank and lay it in the bottom of the tank. When you think the tank is dry and ready, cut one of these beads and see if the center is fully solid. If it isn’t,neither is the seam on your tank! I like to let the silicone cure 4-7 days. I want to be sure it is fully cured before using the tank. The 48 hours recommended on the tube is way too short. I feel a little patience here is needed. The tank is going to be set up for years, I can afford a few days before I start. So there you go. Doing just this I’ve sealed up dozens of tanks. I’ve never had any glass tank that I’ve resealed spring a leak. Work carefully, get the glass clean! and you will be able to say the same.

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