at very low pH value, conductance is mainly effected by [H+]
Conductance at 25°C only [H+]:
pH µS
3,2 239
3,4 152
3,6 97
3,8 62
4,0 39
4,2 25
4,6 10
4,8 6,5
5,0 4
In your case (theoretically): 215 (cond. after water change)-44 (cond. before water change)= 171 (cond. caused by H+) –> pH 3,4
@ yankadi:
all M. kretseri died (this species does not tolerate very low pH, only 2 Paros died). I think a sudden drop of acidity (pH at 3,4) is deadly for Paros too. They tolerate very acid water, if they have enough time to adapt to low pH values. But a is deadly.