There is a lot of speculation and some proof that pH shock is a myth. planted tanks running CO2
during the day have large shifts in pH twice daily. The fish don't go into shock. There is good evidence that what has been blamed on pH shock is in fact osmotic shock, caused by a change in the Total Dissolved Solids (TDS
) of the water. A rapid change of pH from an acid pH below 7 to one above 7 can cause fish to die. It is not the change in pH but, rather, the instant conversion of non toxic ammonium to toxic ammonia. The pH change is often blamed for that too, when the problem is ammonia poisoning.