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RE: [APD] pH shock - Discus and low pH

I'm not a discus keeper, but it is my understanding
that what discus require is low bacterial activity.
Bacterial activity tends to slow-down when pH is
lowered (hence the popularity of mayonaisse prior to
refrigeration) and it ceases around 4.0.  Because
discus come from water with a low pH they don't have
the same immune response to bacteria as fish that 
have been more exposed to bacteria in their home


--- Bill Wallace <bwallace at mitra_com> wrote:
> Secondary affects of pH are a separate matter from
> the pH change itself, as are changes sufficient to
> damage the fish directly.  Examples of these are
> ammonia<->ammonium, or extreme pH changes, eg a ph
> of 1 is likely to cause fishes significant distress,
> but that is regardless of how slowly or quickly it
> approaches 1.  Similarly, the chemical that causes
> the pH change may itself be a problem, but the pH
> change itself not be a problem.  For example, adding
> uranium carbonate in sufficient amounts will kill
> the fish due to heavy metal poisoning and/or
> radioactivity, but not likely due to the pH shift. 
> This whole area of multiple causes and secondary
> affects is what makes understanding these issues so
> difficult, and is often a reason that these myths
> start.  
> Several people have testing ph swings from ph 4.5 to
> 8.5 within minutes, in CLEAN water, ie no ammonia,
> and back again, and the fishes do not appear to
> notice the affect.  That strongly suggests that the
> problems are secondary, not primary.  Still, this
> was with specific fishes, and there might be other
> fishes (eg perhaps those that generate strong
> electrical fields) that maybe much more strongly
> affected.  There just isn't enough information yet
> to know about the affects.
> Similarly, fish like discus that "require" low pH
> levels, may in fact not require a low pH level, but
> only require low concentrations of disolved
> compounds (something that is known to strongly
> affect cells directly, via osmotic pressure), but I
> don't know of any actual studies that attempt to
> figure out what the actual requirements are.  (On
> the other hand, it is entirely possible that it is
> actually low pH levels, and not low disolved
> compounds that is needed - if the problem is that
> the low pH water participates in some chemical
> equilibrium reaction internal to discus.)
> Bill
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