Water & nutrients

Most grow problems trace back to what's in the watering can and how often it gets poured. Start with the right water, then feed to the stage.

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Which water should you use?

Buy a TDS/ppm meter before you buy anything else. Your source water is the baseline every feed chart assumes — if your tap already reads 300 ppm, a "600 ppm" feed is really 900.

Reverse Osmosis (RO)

0–20 ppmBest control

Strips nearly everything out, so you start from a blank slate and every ppm in the tank is a nutrient you chose.
Because calcium and magnesium are removed too, add a Cal-Mag supplement — RO alone will cause Ca/Mg deficiencies, especially under LED.
Wastes a few gallons per gallon produced; store finished water in a food-safe tank so you always have some ready.
Ideal if your tap runs above roughly 200–250 ppm or is heavily softened/chlorinated.

City / Municipal Tap

80–400 ppmUsually fine

Check your city's annual water quality report for hardness, chlorine and chloramine levels.
Chlorine gasses off if you let water sit uncovered 24 hours; chloramine does not — use a carbon filter or a dechlorinator product.
Subtract your tap's starting ppm from your target ppm when mixing nutrients, or you will overfeed.
Hard tap above ~250 ppm is mostly calcium and magnesium — you can often cut back or skip Cal-Mag.

Well Water

150–800+ ppmTest first

Highly variable. Get a lab test or at minimum a TDS meter reading before you build a feed schedule around it.
Often very hard and can carry iron, sulfur or manganese that stain and lock out other nutrients.
Very high ppm well water is best cut 50/50 with RO, or run through RO entirely.
If it smells like sulfur or leaves orange residue, filter it — those minerals will accumulate in your medium.

Water-Softener Output

VariesAvoid

Salt-based softeners swap calcium and magnesium for sodium — the two minerals plants want, replaced by the one they hate.
Sodium builds up in soil and coco and causes lockout you cannot feed your way out of.
Tap into a line upstream of the softener, or run softened water through RO before use.

Distilled & Rainwater

0–30 ppmClean, with caveats

Distilled behaves like RO: zero minerals, so supplement Cal-Mag.
Rainwater is naturally soft and slightly acidic, but can pick up roof debris and contaminants — filter it and don't store it in the sun.
Distilled is expensive by the gallon; practical only for small tents or topping off.

Watering rules that hold

Lift the pot, don't watch the clock

Learn the weight of a dry pot versus a freshly watered one. When it feels light and the top two inches are dry, it's time. A fixed schedule ignores how fast your plant is actually drinking.

Water to 10–20% runoff

In soil and coco, always give slightly more than the medium holds so excess salts drain out. Zero runoff every time is how salt lockout starts. Dump the tray — roots sitting in old runoff rot.

pH after mixing, never before

Nutrients shift pH. Mix everything in, stir, wait a minute, then measure and adjust. Soil wants 6.2–6.8; coco and hydro want 5.5–6.2. Outside that range nutrients are present but unavailable.

Measure your starting water

A $15 TDS meter tells you what your tap contributes before you add anything. Target ppm figures assume you're counting from your source water, not from zero.

Room temperature, oxygenated

Aim for 65–72°F. Cold water shocks roots and slows uptake; warm water above 75°F holds less oxygen and invites root pathogens. An air stone in the reservoir helps.

Ramp up, back down fast

Increase nutrient strength gradually over days. If you see burnt leaf tips, cut strength immediately and water plain once — nutrient burn does not heal, but it does stop.

Wet/dry cycle beats constant damp

Roots need oxygen as much as water. Letting the medium partially dry between waterings drives root growth. Constantly soggy soil is the single most common cause of a stalled seedling.

Feeding by stage

Ranges, not gospel. Every strain, medium and nutrient line differs — start at the low end of each range, watch the plant for two days, then adjust.

Germination & Sprout

No N-P-K

Strength: 0.0–0.2 EC (0–100 ppm)
pH: 6.0–6.5 soil · 5.8 coco
Water: Plain pH'd water only

Additives

1Nothing but clean water — the seed carries its own food for the first days.
2Optional: a light kelp or humic soak at quarter strength if you use a starter plug.

— Keep the paper towel and cup soak in the dark and use room-temperature water, not cold.
— Mist rather than pour; a soaked plug drowns a taproot fast.

Seedling (weeks 1–2)

Light, balanced (e.g. 2-1-2)

Strength: 0.4–0.8 EC (200–400 ppm)
pH: 6.2–6.5 soil · 5.8 coco
Water: RO + Cal-Mag, or low-ppm tap

Additives

1Quarter-strength base nutrient once the first true leaves open.
2Cal-Mag at 0.5–1 mL/gal if you run RO or distilled.
3Mycorrhizae at transplant to colonize the young root zone.

— Water in a small ring around the stem, not the whole pot — this pulls roots outward.
— In soil, most seedling problems are overwatering, not hunger.

Vegetative

Nitrogen-heavy (e.g. 3-1-2)

Strength: 1.2–1.8 EC (600–900 ppm)
pH: 6.2–6.8 soil · 5.8–6.0 coco
Water: Any source at or under ~200 ppm starting TDS

Additives

1Full-strength grow base, ramped up over two weeks — never jump straight to label max.
2Cal-Mag 3–5 mL/gal under strong LED, which drives higher Ca/Mg demand.
3Silica for stem strength — always add it to the water FIRST, before anything else, or it will bind with your other nutrients.
4Beneficial bacteria / compost tea in organic soil.

— Water when the top 1–2 inches are dry and the pot feels light. Weight beats a schedule.
— Feed to 10–20% runoff to flush accumulated salts out of the bottom of the pot.

Early Flower (weeks 1–3)

Transition (e.g. 1-2-3)

Strength: 1.6–2.0 EC (800–1000 ppm)
pH: 6.2–6.8 soil · 5.8–6.2 coco
Water: Same as veg

Additives

1Taper nitrogen down and bring phosphorus and potassium up as the stretch finishes.
2Keep Cal-Mag going — stacking flower is a heavy calcium consumer.
3Optional bloom booster at low dose; more is not better and burns tips fast.

— Plants drink noticeably more during the stretch — check pots daily.
— Watch for clawed, dark green leaves: that's leftover nitrogen, not a deficiency.

Late Flower (weeks 4–7)

P-K heavy (e.g. 0-3-4)

Strength: 1.8–2.2 EC (900–1100 ppm)
pH: 6.2–6.8 soil · 5.8–6.2 coco
Water: Same as veg

Additives

1Peak bloom feed, then begin easing back in the final two weeks.
2Magnesium and sulfur support terpene and resin production.
3Drop any nitrogen-heavy supplements entirely.

— Slight fade and yellowing of lower fan leaves at the end is normal, not a failure.
— If runoff ppm climbs well above what you feed, you have salt buildup — plain-water flush the pot.

Flush & Finish (final 7–14 days)

None

Strength: 0.0–0.4 EC (0–200 ppm)
pH: 6.0–6.5 soil · 5.8 coco
Water: Plain pH'd RO or filtered water

Additives

1No base nutrients. Plain water, or a flushing agent if you use one.
2Enzyme products can help break down leftover salts in the medium.

— Water to heavy runoff a few times to pull residual salts out.
— Flushing is optional in living/organic soil — those pots self-regulate.

Quick troubleshooting

What you see	Likely cause	What to do
Burnt, crispy leaf tips	Nutrient strength too high	Cut feed strength 25–50% and water plain once.
Droopy, dark, heavy leaves	Overwatering	Let the pot dry until it feels light before the next watering.
Droopy, thin, papery leaves	Underwatering	Water slowly to 10–20% runoff; recovery takes a few hours.
Yellowing from the bottom up	Nitrogen shortage (normal in late flower)	Feed in veg; in late flower it's expected fade.
Rust-brown spots on fan leaves	Calcium or magnesium shortage	Add Cal-Mag, especially on RO water under LED.
Runoff ppm far above feed ppm	Salt buildup in the medium	Flush with plain pH'd water until runoff drops.
Deficiency symptoms despite feeding	pH out of range, nutrients locked out	Check pH after mixing and correct to your medium's range.

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