pH adjustment calculator
No chart can tell you how much pH down a reservoir needs, because that depends on your water and your nutrients. A small test dose can. This calculator scales your test up to the whole tank.
Your test dose
Take a measured sample from the reservoir. Add a small measured amount of the same pH up or down you will use, stir, and read the pH again.
How it is calculated
The test dose tells you how far a known concentration of the adjuster moved your solution. The calculator scales that to the change you want and to the whole reservoir:
mL = volume × (test mL ÷ sample) × (target − pH now) ÷ (pH after test − pH now)
This assumes the pH moves in proportion to the dose. Over the small step a test dose covers, in a buffered nutrient solution, that is close. Over large changes it is not, because buffers resist and then give way all at once. That is why the result says to add three quarters first.
Doing it safely
- Adjust pH after the nutrients are in, because nutrients move pH themselves
- Add the adjuster to the reservoir, never water into concentrated acid
- Circulate for 15 to 30 minutes before you trust a new reading
- Wear gloves and eye protection; pH down is usually phosphoric or nitric acid
- Calibrate the pH meter regularly, because a drifting probe makes every dose wrong
Common starting points
These are the targets growers and extension guides commonly quote. Treat them as rules of thumb: crop, cultivar and stage all move the useful number.
| Growing medium | pH range |
|---|---|
| Hydroponics and deep water culture | 5.5 to 6.5 |
| Coco coir | 5.8 to 6.3 |
| Soil | 6.0 to 7.0 |
Status: Cultidock's controller has two pH pump channels, but automatic pH correction is planned, not built: today dosing is manual or scheduled. When it comes, it will dose in steps with mixing waits, the same way this page tells you to. The dosing pump