If roots are sitting in the solution, a rising pH is normal. A healthy, nitrate-fed CropSalt reservoir climbs as the plants feed. We set 5.8 by hand and let it rise to 6.2 before bringing it back down, or hold about 6.0 on a controller. If the tank only stores feed for pots, no roots are feeding from it, so the rise is coming from something else: CO₂ leaving the water, alkaline water still using up acid, a mix that hadn't finished dissolving, or an additive.
| What you see | Usual cause | What we do |
|---|---|---|
| Steady rise in DWC or a recirculating system | Plants feeding | Adjust back to 5.8 at 6.2, or hold 6.0 on a controller |
| Rise in a storage tank with an air stone or pump running | CO₂ loss and pump heat | Mix well, then cut unnecessary agitation |
| Rise right after a refill | Water alkalinity | Mix the full feed first, then adjust in small steps |
| Swings, cloud or film after adding silica | The additive | Leave it out, clean, remix |
| Controller keeps dosing and overshooting | Unfinished mix or probe placement | Let it dissolve and mix before dosing |
Roots in the solution
Nitrate uptake makes the solution around the roots less acidic, so pH goes up as a healthy crop feeds. That's not a reason to change nutrients. Read EC at the normal operating level too; if the tank is concentrating as the water drops, top it off rather than adding nutrients because the pH moved.
A pH that keeps falling is the one to worry about. Check for a mixing error, too much pH down, contamination or declining roots. More in using CropSalt in DWC and recirculating systems.
Air stones, pumps and heat
When dissolved CO₂ escapes, pH rises. Air stones, splashing returns and constant surface agitation speed that up, and a pump that warms the water adds to it. The meter can be reading correctly while the number keeps moving.
Mix stored feed thoroughly, then skip the unnecessary agitation. We use wavemakers to circulate during mixing and pH dosing, aimed below the surface. In DWC, keep the aeration the roots need.
Alkaline water
High-alkalinity water keeps using up acid after the first adjustment. Mix the complete feed before you set pH. Use RunClean in place of pH down: add a little at a time, let each addition mix through the tank, and recheck until you reach target pH. If the same recipe suddenly needs a lot more pH down, check whether your water source or RO blend changed. See water pH, alkalinity and hardness.
Silica and other additives
We don't use added silica with CropSalt. If pH swings, clouding or a film start only after silica goes into an otherwise stable recipe, take it out. Empty and clean a tank with fallout and mix fresh without it. Forcing a cloudy mix back to target pH won't put the material back into solution.
Controllers chasing an unfinished mix
Let the nutrients dissolve before you set pH. Cake takes longer in cold water. We run a Bluelab pH Controller Wi-Fi with RunClean as pH down and a wavemaker to spread each dose. Put the probe away from the dosing outlet and let each dose mix before the next one. Its single dosing pump runs one direction, pH down or pH up.
If it overshoots, check the dose settings, the delivery tube and the mixing. If the reading is erratic or won't settle, clean and calibrate the probe, and replace it if it won't hold calibration. See why your pH meter keeps drifting.
Keep concentrated RunClean, pH up and bleach separate. Never mix concentrated bleach with RunClean or another acid; it can release chlorine gas.
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