Is Cinderblock safe to use in water?

[Salt Addiction]

Hey all,

Fallowing one of the 125s for the next 80 days and I was wondering if anyone has used cinderblocks before on their sides to create caves for fish in a QT tank? Looking for something easy to move when it comes time to move them back to the display again but I have several large fish that may get territorial in a typical empty QT tank. I do have copper in this QT tank and aside from the tank itself I would not be using them after. I ask because currently I have several sitting around my house for another stand project not getting use.

 

[LeftyReefer]

I would not put cinderblocks in your tank. I would think some type of mineral would leach off but who knows.

I'd just use PVC or flower pots instead. something inert.

 

[WVNed]

Cinderblocks are made from concrete and will screw the pH all up.

 

[Jib]

I would be worried about the efflorescence from the cinder block. It would leach salt and other minerals into the water. Not sure if this would hurt the fish or not...I wouldn't risk it.

 

[|Frank|]

I know from making rocks for my aquarium it’s recommended to use Portland cement. If there’s a way to see if that’s the cement used for the cinder blocks you should be good.

edit: my rocks were also cured for a period of time

 

[Salt Addiction]

Cinderblocks are made from concrete and will screw the pH all up.

Makes sense. The same true for red brick then?

 

[jda]

I would check any kind of earthen material for it's ability to bind copper, like aragonite, dolomite and calcite do. Limestone will and I have heard that terra cotta will too (just heard, not confirmed). I do not worry so much about them messing with water chemistry, but they might.

I would stick with PVC, ABS or the like.

 

[WVNed]

Makes sense. The same true for red brick then?

Fired clay should be fine. I have used red brick in an aquascape and it was fine. Fired clay flowerpots would be okay too.