Strange pH problem in flowering stage, changing to tap water from RO

Hi all

My first grow ever, I have a 9 week old autoflower in DWC in its flowering stage and I have been using RO water with added Calmag and Flora Trio nutrients its whole life (around 1/3 of the recommended dosage), no issues. Around 2 weeks ago I started getting sudden pH drops, it would go from 6.2 to 4.8 every 24 hours, yet the plant was growing nicely still. I ruled out Pythium and Algae, I did a res change twice and adjusted nutrients to no avail, the pH kept dropping, whilst still drinking a lot of water and the PPM fluctuating up and down by around 50 ppm daily.

Last night I decided to do 2 things, I defoliated the plant and switched from RO water to Tap Water and removed CalMag and instead added Hydrogaurd. My average water temp has been 24C and the humidity has been getting quite high, in the 60% range, and i couldnt keep it consistent between 40 to 50%.

Last night after defoliating and changing to tap water, 20 hours later my pH has gone down from 6.2 to 6.1 and the humidity has been consistent all day, around 42%.

Im hoping this has resolved the issue, has anyone had any similar experiences and will the change of water affect the plant? My tap water here is 300ppm but I let it sit for 24 hours with an airstone inside before using it.

how big is your res/dwc pot? sounds to me initially like you don't have enough water to buffer the plant's thirst needs

Lately I heard a lot of problems with the ph swinging the only I can think is there is an contaminate in an additive

Something is a little odd. Generally speaking after you mix your nutes your pH should not be far off from where you want it. What was the pH of the water before and after mixing a batch. Did you have to put up or down in? I would expect it to raise as the plants eat the food. If it is going down that is usually bacteria or your pH pen is broken.

i have to use 2 ph pens because they've been notoriously unreliable for me

principlesarelife said:

i have to use 2 ph pens because they've been notoriously unreliable for me

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Do you calibrate them?
If you do and 1 is still giving weird number, then throw it in the bin.
If you calibrate in 4.0 fluid for example and it shows a different number after you put in the 4.0 fluid an hour later, it is useless.

What kind of water? Town, city, well water? Can be the type of filtration each separate one uses could make it high in certain minerals

Keesje said:

Do you calibrate them?
If you do and 1 is still giving weird number, then throw it in the bin.
If you calibrate in 4.0 fluid for example and it shows a different number after you put in the 4.0 fluid an hour later, it is useless.

Click to expand...

i do but one is definitely overdue for a calibration