Are Cement Blocks Safe to use with fish?

[chesterfieldzoo]

I hardly worry about the effects of concrete cinder blocks. My whole 10,000 gallon pond is made from 10 yards of concrete. It is 10 years old. My koi are 2 feet plus long and there are 60 of them in there all year round.

 

[fishdance]

The texture of blocks can be very rough so depending on your fish, this can be another worry. I have seen lots of damaged eyes and scrapped sides on flighty fish or fish which like to `flick` on things.

 

[Oddball]

Concrete mix has differences to cinder/cement blocks. Block manufacturers are free to employ additional "ädditives" as binders/strengtheners to their admixture. And, they're not required to list which additives have been used.