Do I need to reseal this tank? - The Planted Tank Forum
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post #1 of 5 (permalink) Old 08-13-2018, 04:24 PM Thread Starter
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Hi, I'm new to the aquarium hobby and this is my first post here, so please be patient with me. 🙂

I bought a used 50g aquarium on Kijiji. The photos looked nice so I asked my husband to go check it out for me since the seller was on his way to work. Once he brought it home, I noticed it has some black mold growing on the silicone and the edges look a bit frayed (see photo).

Do I need to reseal this? I've browsed some posts on resealing and I'm confident I could do it (I recaulked our bathroom), but some posters said that resealing only the outer layer of silicone without dismantling the entire aquarium actually makes a weaker seal. Is this true?? I'm not willing to dismantle the whole thing.

It looks like the best thing to use is rtv, right? I can't find momentive rtv 108 for sale in Canada. Can anyone tell me if another brand will work just as well? I can get permatex rtv here, had anyone used that?

Finally, the tank is tempered glass. Is using a utility knife to remove old silicone going to risk scratching it up? Would a putty knife work?

Thanks in advance for responding to all these questions!

Last edited by Erin514; 10-21-2018 at 02:43 AM. Reason: Remove photo
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post #2 of 5 (permalink) Old 08-13-2018, 04:45 PM
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I don't know about tempered glass but I always use a razor blade when removing the old silicone. Haven't noticed any scratches yet.

I also don't know anything about rtv haha. I normally just use clear GE Silicone I and make sure there is no mold inhibitor, as that can lead to issues down the road.

I recently just discovered a new type of silicone at Home Hardware that actually says it's aquarium safe on it. The GE Silicone I that I use specifically says it's not safe to use below the waterline in an aquarium, but it seems the general consensus is that they only say that for liability reasons.

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post #3 of 5 (permalink) Old 08-18-2018, 01:39 PM Thread Starter
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Thanks for your reply MCFC.
Does anyone have any advice on using regular silicone vs rtv and what brand would work?
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post #4 of 5 (permalink) Old 09-06-2018, 08:44 AM
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Hope my reply isn't too late on this... Just redid the seals on a 35 gallon hex tank not too long ago. You'll have to redo all of the seals, because new silicone won't stick to old silicone. I used a razor scraper and a lot of patience to get all of the old silicone off, being very careful to keep the razor from slipping between the panes of glass. You don't want to pull the glass apart, you want the adherence between panes to be untouched. Most of the problems with silicone seals are the bits that are visible and touchable, the glass-to-glass stuff is usually fine. Then I rubbed the areas down really well with alcohol to clean off any residue, and resealed with tank-safe silicone I picked up at the hardware store. Let cure (outside! it REEKS of vinegar) for 24 hours, and then test the tank for leaks. (which also rinses the tank well) Good luck!
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post #5 of 5 (permalink) Old 09-09-2018, 08:13 PM Thread Starter
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Thanks for the reply! Better late than never. I did end up resealing two weeks ago and I just refilled the tank a couple days ago to rinse it out and check water tightness. So far it looks good, no leaks.

In case this info is helpful to anyone, to I did use rtv instead of regular silicone because I'd read in old threads that it is stronger and I wish I hadn't because it was sooooo much harder to apply and smooth down than regular silicone. The finished seam is lumpy with a lot of bubbles and I hope it doesn't become a problem.
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