Grow Mediums Hi Just wanted to understand what is causing the nutrient reservoir to rise in pH during the day?

[jumper114]

Hi

Just wanted to understand what is causing the nutrient reservoir to rise in pH during the day?

I use RO water, tested to 12ppm.

It is stored in 25L, food grade, plastic gerry cans, heated to 20C and aerated with a couple of air stones.

It is outside, with the screw lid resting on top - due to tubing.

I grow in coco.

The reservoir feeds a drip irrigation system and is stored outside. A pump feeds the irrigation system in the tent.

I assume it is being caused by a reaction with the air? But why?

In 24hr it drifts from EC 0.6, ph 6.0 -> phH 6.9 (with calibrated bluelabs pH pen)

thanks

 

[Muddy]

It's likely the aeration. The added desolved oxygen in the water raises it's pH. I prefer to premix my nutrients at least a day ahead, aerate over night, then adjust the pH the next day. Also, RO doesn't have much buffering capability since all the trace elements are removed. Adding some baking soda can help to restore buffering but be aware that baking soda will also raise the pH.

 

[jumper114]

You are spot on.

I tested with and without cal mag. Sealed and not sealed.

Sealed pH no change 6.3. Open to air 5l goes to 6.7 overnight. Cal mag without always .1 below.

With air stone 7.1 overnight. Both the same.

All solutions made to 0.6 EC

As such airstones in nutrient reservoirs require pH auto calibration for optimal results

 

[Death The Cultivator]

You are spot on.

I tested with and without cal mag. Sealed and not sealed.

Sealed pH no change 6.3. Open to air 5l goes to 6.7 overnight. Cal mag without always .1 below.

With air stone 7.1 overnight. Both the same.

All solutions made to 0.6 EC

As such airstones in nutrient reservoirs require pH auto calibration for optimal results

If your drip system has an anti siphon valve or even if it doesn't you won't really need to aerate your reservoir. My last grow I stopped doing it and was able to stop chasing ph.