# DIY Background - how long until safe?



## kme38 (Sep 9, 2008)

Just had a go at my first styrofoam/quickdry concrete background. Love the look of it, I am going to apply my final coat tonight after work. To make the concrete safe for the tank, how long must I soak/leave it submerged in water?

I have a large water storage tank in my yard I can leave the background in to soak - or does it have to be cycled with fresh water regulary?

Obviosly the safety of my pets is paramount so dont want take any risks?? :-?


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## trigger (Sep 6, 2002)

It's safe as soon as it stops leeching stuff into the water making it harder. So you'd need to change water every nown and then to see if it still raises the water values too much.


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## Drowned (Mar 16, 2009)

Hi.

Can you give me a hint what kind of concrete you used? Does it have to be something special?


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## Mcdaphnia (Dec 16, 2003)

Unless you used a hydraulic cement (cures underwater), the background needs to first cure in the air for about 30 days in a moist environment (misting with water or loosely wrapping with plastic). Excess alkalies can then be rinsed off. The soaking period is misunderstood as a leaching process but the important thing happening then is the same as cycling a filter. An air stone or minimal water circulation and very little water changing helps out. Depending on how much ammonia and oxygen are present to feed the good bacteria, after a week or two of soaking, the surfaces of the background are coated with bacterial colonies that seal off the background from leaching into the tank water.


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## trigger (Sep 6, 2002)

Mmm, I just used the "add water" kind of cement. And at first i just put it outside in the rain. Plenty of fresh water over it. After that I placed it in the tank and did a bi-dayly water change for about two weeks.


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## Mcdaphnia (Dec 16, 2003)

trigger said:


> Mmm, I just used the "add water" kind of cement. And at first i just put it outside in the rain. Plenty of fresh water over it. After that I placed it in the tank and did a bi-dayly water change for about two weeks.


 "the "add water" kind of cement." That is cute! Not very specific since all concrete has to hydrate, but very cute! What I take from that is concrete is reconstituted limestone, with some sand and/or gravel added, and maybe specialty additives for all kinds of uses from mundane to bizarre. It can be made porous so that rainwater filters through it to avoid a flooded parking lot. It can be made so light that it floats, and in that form it could be used as insulation or as a raft or boat frame.

It is tough stuff, so even if you do things extremely wrong in terms of what is known about the art and science of concrete, the material may still turn out fine. It takes quite a lot to mess up concrete.


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## Drowned (Mar 16, 2009)

Is it possible that the ordinary kinds of cement has some additives like some kind of fungicide etc that can be harmful to the fish?


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## trigger (Sep 6, 2002)

Drowned said:


> Is it possible that the ordinary kinds of cement has some additives like some kind of fungicide etc that can be harmful to the fish?


Not sure, but if it does, it would definitely be noted on the bag/box.


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## Mcdaphnia (Dec 16, 2003)

Drowned said:


> Is it possible that the ordinary kinds of cement has some additives like some kind of fungicide etc that can be harmful to the fish?


Strobilurin, chlorothalonil, and didecyl dimethyl ammonium chloride are some fungicides that might be in coatings later applied to cement after it's cured, but ordinary cement is not going to have them mixed in. Plus I'm not sure just how harmful those might be to fish since they are usually incorporated in some kind of waterproof coating. Best to avoid using them for aquarium items.


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