I have a Tropical fish tank I got a foam backing for it could anyone give me a tip how to clean the foam?

Answers:
try turning the filters down a bit have you put any chemicals in there like treatment or cycle .that could be the problem ..hope you solve it ..

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Rinse it in rainwater, not water from the mains.

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I kept tropical fish for several years but never had a 'foam backing'.
I had polystirine underneath it to create an even surface so the glass didn't crack.
I had a aquarium scenery backing poster stuck to the outside of the back of the tank to enhance the depth %26 create a more interesting scene.
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Oh I see it's for breeding . never bred fish myself, apart from guppies.

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Foam backing? Does it go on the outside or the inside? Please add more info on this "foam" backing. Is it closed cell or open cell?

Outside: Both open and closed cell, mild soap and soft cloth.

Inside: Closed cell only, vinegar and soft cloth or salt paste on wash cloth. Rinse well before replacing in tank.
Open cell, just rinse in clean water. You don't want chemicals trapped in the open celled foam.