Grow Mediums Got my first PH pen. Questions for usage in coco with hydro rez nutes

[lunarman]

My tap water is around PH 7.2.
And I'm using coco with some perlite in autopots.

I have a control wizard PH probe that I have been using for months and it is great. I was testing my water with the liquid PH fluid and was adjusting it down to around 6 then watering. I was using an organic amended coco in fabric pots before, not autopots and liquid nutes in a rez. I would measure the coco medium once in a while with the probe and it was generally around 6.5 based on the probe readings.

The local hyrdo guy I bought the HM Digital PH-80 meter said that I should PH down my water down to 6.5 and measure/confirm with the meter. Then he said add my nutes according to the schedule and that will bring it down even further. And that I don't even need to measure PH again using the meter. I just need to put the water/feed in the rez and don't worry about it.

Is this really the way PH the feed water?

 

[KonopCh]

I think it's not needed to lower pH of water first. Just add nutes and they will lower your pH. Than adjust with pH solution - it's needed only a little.

 

[lunarman]

I think it's not needed to lower pH of water first. Just add nutes and they will lower your pH. Than adjust with pH solution - it's needed only a little.

The guy also told me not to put the pen in the water that has nutes in it. He could not tell me why though. Is it ok to put the pen in the water with nutes?

And now that I have the pen and am taking frequent readings I noticed something. I had 3 gallons of water I ph'd down to 6.5 last night. When I checked again this morning it was like 7.1 or something. Can PH value increase overnight?

 

[KonopCh]

Yes, pH can go up overnight. If you have airstones also.
But mine goes up by 0.1 and over 5-7 days only goes up by 0.4 maybe. I use AN nutes in RO water.