re: cinder blocks

---------- Forwarded message ----------
Date: Wed, 25 Sep 1996 09:20:15 -0700
From: Kevin Kelley <kkelley at cdpr_ca.gov>
To: aquatic-plants at actwin_com
Subject: re: cement bricks, regular bricks, and cinder blocks

I have for many years used cement bricks (cinder blocks) in my
aquariums.  I have had little problem since I have kept them only with
Central American (CA) and African (mbuna) cichlids.  The large CA
cichlids (Cichlasoma dovii, C. friedrichsthali, etc.) use them as caves
for spawning, and for hiding purposes.  The mbuna are a little too small
to successfully defend the openings in the 8"x8"x8" or the 8"x8"x16"
blocks.  However, if you can get the 12"x12"x2" blocks with the rosette
or square inside patterns, and silicone 2 or 3 together, they do make
interesting condominiums for the mbuna, and the smaller CA cichlids. 
I've had numerous spawnings in these condominiums.  (One can smear
the visible [and dry] surfaces of the blocks with silicone and press them
into dry natural gravel or sand for a more natural look.)

One caution however, is that if your fish extensively dig into, or move
the substrate (i.e. CA and African cichlids) use them only in a bare
bottom tank.  I learned this the hard way, as one day I watched one of
my C. lentiginosum meet his unfortunate demise as a condominium he
was busily digging under fell over on top of him.  

As for affecting the water chemistry, they may, depending on the
original chemistry of your water supply.  Cement/concrete is essentially
calcium carbonate (crushed up oyster shells), is moderately basic, and
will attenuate water pH towards 8.5+.  However with regular water
changes (50%+ weekly), this should not be a problem.  The CO2
generator will help establish and maintain a pH in the range you wish, if
you don't have other water chemistry problems (i.e. lots of decaying
matter).  If  your water supply is acidic or if you are trying to raise
Apistogramma sp. then you may/will have problems.  If your tap water
is pH 7.5 to 8.0, you will probably find that your water supplier is
already using calcium carbonate.  

With regards to cinder blocks releasing toxins, I have no idea.  Certainly
my Central American and African cichlids do not object to anything that
might dissolve from the blocks.  And, I have friends that raise discus in
tanks with regular bricks.  I would recommend however, that when
purchasing bricks or cinder blocks, you make sure that they were not
stored anywhere near any pesticides or household chemicals the store
may also sell.  [There is one store here (in Sacramento CA) that stores
cinder blocks about 20' from their pesticide display (way too close for
my comfort).]  I would also recommend that you do not use bricks or
blocks from around the house for the reason that you do not know their
chemical exposure history.

With regards to soaking bricks or cinder blocks, you have little to lose
but time.