Size of pH chemical additions

[Aqua Lab Rat]

The typical instructions for raising or lowering pH say to add X amount, then retest later. I assume that is so that you don't over-adjust or end up "see-sawing". (That said, I have never overcorrected, it always seems like the doses are about half as much as they should be.)

Outside of the over-adjustment / under-adjustment issue, and possible cloudiness if you bump the pH up too quickly, is there some other reason to make smaller adjustments, such as creating toxic gasses?

 

[JoyfulNoise]

For pH adjustments, you need to consider equipment. If you make a large pH adjustment with acid and accidentally mess up the measurement, then you could lower the pH below 7.0 or, worse, crash the TA and have the pH drop precipitously. That is REALLY BAD for anything metallic in the water because pH is the dominant factor in corrosion of metal parts (dissolved oxygen content is the next biggest issue for corrosion). As well, for increasing pH, going too far too fast can mean scaling out calcium carbonate into your equipment. Filter elements can get "limed up" with calcium scale and gas heater cores can develop scale leading to blockages and reduced flow.

Slow & steady is ALWAYS BETTER than fast & loose when it comes to chemistry....

PS - And no, you will not create toxic gasses....

 

[Aqua Lab Rat]

So it is more for the potential corrosion / scaling issues. Makes sense. Some dosing instructions I have seen put overly strong emphases on it like "DO NOT EVER ADD MORE THAN X" as though it would mean fires, explosions, or Armageddon. In my case, I'm often adjusting test tanks or test spas. In those cases, I'm not too worried that I'll destroy anything but do need to adjust the pH quickly or often to keep it in range for the test. For a consumer who checks things once a week, though, I can definitely understand the reasoning and the need to bring the potential downside to their attention.