TDS and pH

[PaulineMi]

I was looking up info on the effects of moving fish from a tank with high TDS to one with a lower TDS.  My aged RO/tap mix reaches the same pH as the tanks it's going into.  I have slowly been lowering the TDS but the pH hasn't been affected.

I've read both anecdotal and scientific stuff explaining that going from low pH to higher pH is okay.  However now I'm finding that it's actually the TDS change that causes problems and that fish can handle pH changes of even 2 as opposed to the no more than .5 normally accepted. It seems that both schools of thought are based on the osmotic pressure changes.

I'll go look for some links to articles I read yesterday. In the meantime I'm wondering if anyone is familiar with the two schools of thought. I'd be inclined to think that they go hand in hand if I didn't see a big change in TDS but none in pH with my RO blend. I have a friend who experiences the same thing.

[PaulineMi]

Here's one of many articles I've found that addresses osmotic shock and TDS:

http://www.plecoplanet.com/forum/showthread.php?t=3480

[Mugwump]

I've read some similar articles, Pauline. My feeling is that there are most likely more things that will affect the tds, than PH. If we forget the PH difference, if not radical, what will the fish experience first?.....real high tds difference is immediately noticed by the fish, lower tds differences should be like a 'breath of fresh air'.....wouldn't you think??

your article talks of low PH fish and water...acidic....there, yes, it would be more of a concern

[BillT]

Different fish can tolerate different kinds of changes.
Some fish are able to take rather large osmotic changes (consider brackish fish in a estuary during a tidal change or salmon going upstream from sea to river).

I regularly take young juvenile danios and and transfer them from conductivity of 10500 ?S to 500 ?S over period of an hour.