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My son and I are so close to cycling. Everything set up, except there is a 2 inch hole in the back lower corner of our fish tank, that was pre-cut in the tank when we got it. I had tried to seal it by adhering 2 four square-inch pieces of plexiglass (one inside, one outside) over the hole using an aquarium rated silicone sealant bought online. The plexiglass was not thick, bought at local hardware store. This didn't work. After a few days of having water in the tank, it began to leak through my fix. So, my question is: any suggestions on how to seal this hole? Is there a bulkhead gasket that has a cap/is closed? Is there a silicone sealant that is fullproof underwater? Any feedback would be greatly appreciated.

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Put a bulkhead fitting in the hole and then cap the fitting off.  Use a fitting that is slip and then just insert a small piece of pipe and glue a cap on the end.

You could use a uniseal too and the same appraoch Bob mentions.

Hi Brooks,

I had the same but as a 1" hole. You can use a 2" bulkhead with rubber gasket on the outside, male adapter and end-cap on the outside. I used my spares...... male adapter on the inside to female adapter on the outside. 1" pipe with an end-cap on the outside. Silicone both the inside and outside........ allow the silicone gaskets to dry completely before tightening.

If the hole is exactly 2" in diameter... a 1-1/2" FIPT/FIPT bulkhead fitting might be the way to go. To install a 1-1/2" bulkhead through a tank wall, you need a 1-3/4" hole... the flange should be able to swing it if your hole is 2"...but more than that would be pushing it. (the alternative is to widen the hole to 2-3/8" and use a 2" bulkhead). 

If you purchase a 1-1/2" FIPT/FIPT bulkhead you can plug it off with a MNPT plug such as this...http://www.aquaticeco.com/subcategories/3664/Plugs-MNPT

or cap it off with one of these caps...http://www.aquaticeco.com/subcategories/884/Caps-FNPT

If your tank wall is much more than 1/2" I'd use a bulkhead like this one this...http://www.aquaticeco.com/subcategories/4972/Bulkhead-Fittings-Economy

If my tank wall was 1/2" or less I'd sooner go with something like this one...http://www.aquaticeco.com/subcategories/834/Bulkhead-Fitting

I've used both types, and I really like that last one because of how the nut is designed...it's much easier to get a handle on it to tighten...and it comes with 2 rubber washers and a cork one. (At least mine did)...

Here's a product key so that you know what those F-B-D-L letters mean...

3M makes a polyurethane sealant/adhesive (it's both) that is formulated to cure under water. I've been using it like mad in the AP greenhouse. So far so good. It's called 3M E5200. They make an E4200 which I hear is the same, only it fully cures in 24 hours instead of 7 days. People who own and repair boats for a living say the E4200 is slightly weaker than the E5200, but for your application I'm sure it would do. I've only used the E5200 so that is the one I can recommend.

Good luck Brooks...

Thanks everyone. I really appreciate it. Once again, this forum has been very helpful.

 

oops here's that product key...http://www.aquaticeco.com/images/static/charts/BK112-chart.jpg

These things are sized similar to how pipes are are...meaning inside diameter...the letter 'D' indicates the size the hole would need to be to accommodate the outside diameter of the fitting...

Brooks, if the tank is glass, try your patch method exactly like you did only using a glass square instead of plexi. Clean both surfaces with alcohol first, it will seal like a charm. If your tank is acrylic, use an acrylic patch the same thickness as the tank, and adhere it with acrylic solvent, both patch and solvent are very cheap at your local plastics house. Around here, these are available at TAP plastics. Personally, I wouldn't use a bulkhead fitting unless you want a bulkhead in that spot.

So Jon, do you think the reason my fix didn't work is that the patch wasn't as thick as the tank? Because it definitely wasn't, and it wasn't the same material. The tank is acrylic, and I just bought some cheap plexiglass at the hardware store. I would much rather do the fix you suggest as I think it will be simpler and more full-proof.

Jon Parr said:

Brooks, if the tank is glass, try your patch method exactly like you did only using a glass square instead of plexi. Clean both surfaces with alcohol first, it will seal like a charm. If your tank is acrylic, use an acrylic patch the same thickness as the tank, and adhere it with acrylic solvent, both patch and solvent are very cheap at your local plastics house. Around here, these are available at TAP plastics. Personally, I wouldn't use a bulkhead fitting unless you want a bulkhead in that spot.

Brooks, your patch didn't work because of the silicone. Silicone sticks like ninja to glass, but not acrylic. To patch acrylic (plexi-glass IS acrylic), you should use the solvent cement made for the purpose. It is thin and clear like water, and is usually applied with a syringe-tipped squeeze bottle. Capillary attraction draws the solvent between the two layers, and wa-lah. Done. You don't need to do an inner and an outer, just one or the other, but patching both sides is fine too. It needn't be the same thickness, but should be thick enough not to deflect under the weight of the water. Hope that helps

Thanks Jon. That does help. Just want to be sure: I looked on Taps website, and the free-flowing, solvent type acrylic cement is the stuff I want, correct?

Jon Parr said:

Brooks, your patch didn't work because of the silicone. Silicone sticks like ninja to glass, but not acrylic. To patch acrylic (plexi-glass IS acrylic), you should use the solvent cement made for the purpose. It is thin and clear like water, and is usually applied with a syringe-tipped squeeze bottle. Capillary attraction draws the solvent between the two layers, and wa-lah. Done. You don't need to do an inner and an outer, just one or the other, but patching both sides is fine too. It needn't be the same thickness, but should be thick enough not to deflect under the weight of the water. Hope that helps
Yes Brooks. I searched their site, this is the glue:

http://www.tapplastics.com/product/repair_products/plastic_adhesive...

Squeeze bottles to the right under related items. Looks like $10 for glue and bottle, and will do many many acrylic projects. It's addicting and easy, you'll have a new hobby

Thanks Jon. Got it all ordered. I appreciate it.

Jon Parr said:

Yes Brooks. I searched their site, this is the glue:

http://www.tapplastics.com/product/repair_products/plastic_adhesive...

Squeeze bottles to the right under related items. Looks like $10 for glue and bottle, and will do many many acrylic projects. It's addicting and easy, you'll have a new hobby

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