Sudden pH drop - can somebody explain why?

Hi everyone,

I have just set up an automated hydroponic system very similar as the one designed by Kyle. I don’t have any plants yet (still in germination in the nursery), but I’m running tests to make sure that water sensing and pH and EC regulation work as expected.
Since I don’t have any plants yet, last night I disabled pH+EC regulation completely and just let the pump run for a few minutes every half an hour, just to see if the water sensi

ng is stable. As expected, pH and EC didn’t vary during the night, but in the morning, when the pump first started after the grow light went on (5:00AM) there was an extremely sudden drop in pH from 6.0 to 4.1.

Does anyone have an explanation to that or has had a similar experience? What could have caused that and how I can avoid it in the future?
Of course, if the regulation had been active, it would have reacted - but still, I think it is important to understand what happened there.
Thank you!

You likely haven’t isolated the power to your sensors. With aquatic systems that have pumps or multiple sensors, you will likely have interference issues if you don’t isolate.

Hi, thank you for your reply!
I don’t think that that’s the problem, I am using atlas scientific sensors, which are isolated. To reduce cost and for ease of installation I bought this kit (Wi-Fi Hydroponics Kit | Atlas Scientific) but removed the ESP32 and connected the i2c bus to the raspberry pi.

Sensors aren’t isolated by virtue of being Atlas Scientific brand. Are you actually using isolation circuits?

Sorry for the misunderstanding. Yes, the kit includes three electrically isolated slots (for pH, EC, and an AUX, which I am not using). They are definitely electrically isolated.

Looking more closely at your y axis, these are not very large changes in pH and EC at each pump event, except for what occurs at 5:20. What occurred differently at 5:20 than the other events?

Yes, that’s exactly my point… there’s a sudden change in pH at 5:20, when the pump starts. The only difference to previous starts (the pump ran for 3 minutes every 30 minutes the whole night) is that at 5:00AM the grow light went on. But that doesn’t explain it to me…
The changes in EC and temperature are not a concern.
Thanks for looking at it!

Of the many pump actions, the pH and EC change drastically close to only one of those pump actions. This indicates it’s not the pump that caused the change, but something else that occurred near the same time. There’s not enough information about your system nor enough data from the graph to determine what is causing it.

Grab your pH sensor and give it a little shake. If you got an air bubble or contamination you could throw your reading off.

I’ve seen the same when I was using an air stone.