# Advice for Sealing Gaps In Background.



## G-Wiz (May 28, 2014)

Need advice for what is safe to use to seal large 2 inch gaps on the background in tank. It is not a straight edge. It is a rock out cropping off of the back of the tank. Its where the background is supposed to meet the bottom of tank. I used silicone on the small gaps . The large gaps are to big for silicone unless I stuff something under it first to fill the void. I'm not sure what I could fill the void with that wouldn't break down from being submerged all the time. Expanding foam would be perfect but not sure if it would be safe or break down. I cant get to both sides to seal it. I've read about pond foam foam but not sure if it needs to be sealed either? It will be at the bottom and covered by sand.
Thanks


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## Kanorin (Apr 8, 2008)

Know that you don't necessarily need a perfect seal. As long as you can cover the majority of the hole (even with something like plastic mesh) to prevent fish from swimming back there.


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## Mcdaphnia (Dec 16, 2003)

Some backgrounds are hollow with a series of voids in back. The gap may be nothing more than a cave, and not need any action at all. If the background is dark, pond foam will safely fill in spots that you want to fill, for whatever reason you have. Once cured it is inert, and it can even be applied above the water line and submerged as soon as it hardens.


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## G-Wiz (May 28, 2014)

Thanks for the replies. So as I understand the pond foam can be used underwater without being sealed and it wont break down over time.


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## Mcdaphnia (Dec 16, 2003)

The pond foam can be used underwater but it is soft, so it can be damaged or chewed on by fish over time, a long time, except for really big aggressive fish.


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## G-Wiz (May 28, 2014)

Thanks again for the replies. This will be covered by the sand so I think it will work perfect.
Thanks


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