Confused about my tap water + PH-down = lowering the PPM

[Jaydot]

Hello,

So from what I've read PH-down is supposed to raise your PPM
The band I use is Nortembio (composed of citric acid -> cido 2-hidroxi-1,2,3-propanoetricarboxílico)

My tap water reads; 0.55EC / 270PPM / 7.5 PH
PHdown to 6.2, then reads EC 0.4 / 210 PPM

Is it because its bio?, some magical brand?, is it the citric acid?
I have no clue but I hope someone can explain this.

Thanks : )