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Re: Low pH problems

J. Daniels wrote:

> I'm looking for some input on how to fix my low pH problems. I've got a
> 108 gallon tank with natural rock and is fairly heavily planted with a
> low fish load (about 25"). The pH is consistently between 4.5 and 4.7.


Actually, I'm a little surprised that you have anything alive in the tank 
at that pH.

Check the buffer capacity in your tap water.  It must be very low.  There 
is no buffer capacity in your tank water at a pH of 4.5.  It appears to 
me that something in your tank is producing a strong acid and that is 
wiping out whatever small buffer capacity your tap water provides.

I can think of two sources of strong acid.  The first is the nitrification
process.  Nitrifying bacteria are a constant source of acid, and the more
you feed the more acid they produce.  Most of us have tap water with
enough buffer capacity that regular water changes are all we need to
offset the pH drop from nitrification.  But, if your tap water buffer
capacity is very low then it won't take much nitrification to drop the pH. 

The second alternative is something I've never read speculated about here,
and I'm not one to let a good speculation just go to waste.  If your
natural rocks include sulfide ores (most likely pyrite - same as fools
gold) then oxidation of the pyrite will produce acid.  Again, if your tap
water buffer capacity is very low, then it wouldn't take very much acid to
drop your pH. 

> I've been
> told there could there be too much aeration which is generating carbonic
> acid. I'm not convinced of this due to the size of the tank and frequent
> water changes. I would have thought the volume of water could buffer the
> amount being generated.

I think to maintain a pH of 4.5 to 4.7 with carbonic acid you probably 
would have to put your tank under pressure and feed it CO2.  If you 
aren't doing that, then carbonic acid isn't the cause.

If the buffer capacity of your water is very low, then you should add
something to the water to increase its buffer capacity.  The easiest thing
to use is sodium bicarb.  I think the APD archives and probaby The Krib
contain information on how much bicarb to use to get the effect you want. 
Commercial preparations for amending RO water would probably also work. 

If you do succeed in raising the pH from 4.7 or so to 6.5+ then I think 
you'll see a lot of changes in your tank.  You probably won't like all of 
the changes.  

Roger Miller