PH Question Aeroponic grow

On 5-12 I started an Aeroponics grow. The unit holds 2 gallons of water. I PHed the water to 5.7 and the PPM was 365.The next morning I checked the PH and it had risen to 6.6. The PPM was stable at 340. So I adjusted the PH to 5.6. That evening I checked the PH again and it had risen to 6.4. So I adjusted again to 5.8 the PPM was stable at 338. This cycle has continued over the last 4 days with the PH rising to 6.2 to 6.4 over a 12 hour period. The PPM stays stable at 330 to 360. So my question is why won’t the PH stay the same. Also I have PHed water before and when I let it set over time the PH rises. Is This normal. I am using RX Green Solutions PH Adjuster Raise/Lower Brand.The Plants are doing GREAT! Just wonder why its doing this.

@Aquaponic_Dumme is an aeroponic grower maybe he can help you out

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Thanks. Have you notice this with water that you PHed and left around for a period of time

It could likely be due to some minerals in the water thinning out or dissipating in the water as it sits

I started out with 2 gallons of RO water. So you are saying the PH solution degrades over time

I think so if it sits 12 or more hours

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Well thats exactly what it is doing. So I will have to adjust every 12 hours. Do DWC do this too

Im pretty positive they do as well yes


Thanks. I learned something new today and thats what its all about. Happy Growing



How long after you add pH down, are you testing the water? This yoyo effect of up and down is very common when dealing with tap water. What happens is this:

*You’re adding pH down.
*Now that your water is more acidic, the"carbonates" within the water, are able to dissolve.
*As carbonates dissolve, they act as an alkaline, and drives pH up.
*As the water becomes more alkaline, the carbonates become more stable, and the dissolution slows or stops.

This will keep happening until all carbonates are dissolved.

To fix:
You can add a RO filter to your system, and removing the hardness (carbonates) from the water, before you mix.
You can wait longer after adding acid, before testing the pH, and reapply acid as needed.

If you choose the latter of the two, keep in mind that, the more you repeat the process, the less carbonates will be, and need to dissolve, and the more effect the acid will have in bringing down the pH. Basically, add less and less acid, otherwise you’ll over correct.

Does this help?


Just to point it out brother he started with 2 gallons of RO water

Is the RO working?

Whats the ppm of the water coming out of the RO, before the mix?

Is there something new in the reservoir driving up the pH, like the hydroton type?

When’s the last time the batteries where swapped out in the pH meter?

When’s the last calibration of the PH meter?

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Here is some good info from the start that may help out, I appreciate you taking the time to help out through this @Aquaponic_Dumme

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@Aquaponic_Dumme So I checked the RO water from the same batch. PPM 37 PH 7.5 before adding anything. Checked cal of PH meter in 4.0 solution it was dead on. Meter is new so its not the batteries. This water comes from a store which has a machine and you fill up your jugs. It is advertised as RO water. I put the blue plastic ice packs in there to keep root temp down. Other than that its is a new system just plastic hoses and a pump. Running 0.0012" brass misters. Plants are in rockwool hanging in 3" net pots.

So I just checked my system and the PH has already risen to 6.0. I had adjusted it down this morning to 5.2. So its rising 0.6 to 0.8 points every 12 hours

Sorry, I’ve been MIA…

any updates?

@Aquaponic_Dumme So here is the update

5-16 Turned off air stone.

5-17 9:30am Ph still rose to 6.0 adjusted to 5.7 ppm370
7:30pm Ph rose to 6.2. Adjusted to 5.7 ppm 370
Turned air pump back on but just pumped air into the root chamber above the water.

5-18 10:30 am PH rose to 6.2 adjusted to 5.7 ppm 360
9:00 pm PH rose to 6.3 adjusted to 5.5 ppm 360

5-19 10:30 am PH rose to 6.3 adjusted to 5.5 ppm 380

This was a test to see if the air stone had any effect on PH. So from the data I feel the air stone has no effect on PH. So I am currently running with the air stone on.
Any Thoughts?