Cannabis grown in hydroponics does best with the nutrient solution held between pH 5.5 and 6.5, and PPM between 200 and 1,200 depending on the growth stage. Clones and seedlings run at 200 to 400 PPM, plants in veg at 400 to 800 PPM, and flowering plants at 800 to 1,200 PPM on the 500 scale. Test both values at least once a day. Fix pH first, then fix PPM.

Buy vs. DIY: Choosing the Right Cannabis Hydroponic System

Prerequisites

  • pH meter or pen, calibrated in the last two weeks
  • TDS or EC meter that reads PPM or EC
  • Hydroponic-grade pH Up and pH Down
  • Calibration solutions: pH 4.0 and 7.0, plus 1,000 PPM or 1.4 EC standard
  • Clean jar or cup for pulling samples
  • Two-part or three-part cannabis nutrient line
  • Reservoir thermometer

pH and PPM Targets by Stage

These ranges assume a recirculating, deep water, or drain-to-waste system with water between 65 and 75 F. Numbers are PPM on the 500 scale that most US meters use. On the 700 scale, divide by 1.4. EC equivalents are listed for growers who read in EC.

read more

  • Clone or seedling, weeks 1 to 2: pH 5.5 to 6.0, 200 to 400 PPM (EC 0.4 to 0.8)
  • Early veg, weeks 2 to 4: pH 5.6 to 6.0, 400 to 600 PPM (EC 0.8 to 1.2)
  • Late veg, weeks 4 to 6: pH 5.6 to 6.1, 600 to 800 PPM (EC 1.2 to 1.6)
  • Early flower, weeks 1 to 3: pH 5.8 to 6.2, 800 to 1,000 PPM (EC 1.6 to 2.0)
  • Peak flower, weeks 4 to 7: pH 5.8 to 6.2, 1,000 to 1,200 PPM (EC 2.0 to 2.4)
  • Ripening and flush, final 7 to 14 days: pH 5.8 to 6.2, 0 to 300 PPM (EC 0 to 0.6)

Plant size, light intensity, and strain all shift these numbers. A plant under weak light drinks less and burns at lower PPM. Treat the ranges as a starting point and read the leaves.

Cheapest Cannabis Hydroponics Setup Buying Guide

Daily and Weekly Routine

  1. Pull 100 ml of water from the reservoir, away from the airstone and return lines.
  2. Rinse the pH probe in clean water and blot it dry.
  3. Record the pH reading in a notebook or app.
  4. Rinse the PPM probe and record the PPM reading.
  5. Record the water temperature and the reservoir level.
  6. Top off with plain water to the original level before you test again for PPM.
  7. Adjust pH to the middle of the range for the current stage.
  8. Adjust PPM only if the reading sits more than 15 percent outside target.
  9. Check roots for slime, brown patches, or odor once a week.
  10. Drain and refill the whole reservoir every 7 to 10 days.

How to Raise or Lower pH

Never pour pH Up or pH Down straight into the reservoir. Dilute it first, or you will swing the solution past your target and shock the roots.

Beginner Cannabis Hydroponics Mistakes to Avoid

  1. Fill a cup with 500 ml of reservoir water.
  2. Add pH Up or pH Down one drop at a time.
  3. Stir for 30 seconds and read the value again.
  4. Pour the cup back into the reservoir near a circulation point.
  5. Wait 15 minutes and retest the reservoir.
  6. Repeat the cup method if the reading is still outside the range.

If pH climbs every day from 5.8 to 6.5, the reservoir is usually too small for the plant size or the water is too warm. If pH drops on its own, the roots may be rotting or the PPM is running too high.

How to Adjust PPM (EC)

  1. Check the reservoir level first. A low level concentrates salts and inflates the reading.
  2. Top off with plain water to the fill line.
  3. Retest PPM after the water mixes for 10 minutes.
  4. Add nutrients in the order the bottle label lists if PPM is low.
  5. Add plain water if PPM is high.
  6. Retest after 15 minutes of circulation.

Watch the trend across three days. A falling PPM with falling water means the plants are eating more than they drink, so raise the feed. A rising PPM means the plants are drinking faster than they eat, so lower the feed.

Common Beginner Mistakes

  • Skipping calibration, which sends every reading off by 0.3 pH or more
  • Measuring pH right after adding nutrients, before the solution settles
  • Chasing a perfect number instead of holding a steady range
  • Mixing pH Up and pH Down in the same cup
  • Using tap water with high alkalinity without letting it sit or filtering it
  • Letting the reservoir run above 75 F, which invites root rot and pH drift
  • Running full-strength flower nutrients on young plants

When to Change the Reservoir

Drain and refill every 7 to 10 days, and sooner if PPM creeps past the top of the range or the water smells off. Between changes, top off with plain water and rebalance. Clean the reservoir, airstones, and pumps with a mild peroxide or enzyme cleaner at each change. Fresh solution plus steady pH and PPM is the single biggest driver of fast growth in a hydro cannabis garden.