Why isn't there a single mL/L number?
The most common mistake is hunting for a chart that says "X mL/L per product per stage" as if it were universal. That number doesn't exist, because it depends on three variables that shift with your setup: your source water hardness (which already contributes EC before you add anything), your substrate (soil, coco, and hydro have different buffering capacities), and your growth stage. A dose that's dialed-in with RO water can be way too hot with hard tap water, or insufficient if you're coming out of a long veg and the plant is carrying a lot of leaf mass.
The right unit for feeding is not mL/L but EC (electrical conductivity, in mS/cm). EC integrates all the solutes in your solution — including whatever your source water brought in — and tells you whether the plant is getting what it needs. The correct protocol is: measure the EC of your base water, calculate how much nutrient to add to hit the target EC for your stage, then verify with your meter before feeding.
What EC should you target at each stage?
Stage-based target EC ranges for indoor cannabis are validated in the scientific literature and are brand-agnostic. Bevan et al. (2021, DOI 10.3389/fpls.2021.764103) documented the effect of different nutrition levels on yield and cannabinoid profiles in Cannabis sativa under controlled conditions. Reference ranges are as follows:
- Seedling / freshly rooted clone: EC 0.6–1.0 mS/cm. Young roots are sensitive; less is more at this stage.
- Early veg (days 1–14): EC 1.2–1.6 mS/cm. The plant starts actively demanding nitrogen and calcium.
- Late veg (day 14+): EC 1.6–2.0 mS/cm. You can ramp up gradually as the plant builds mass.
- Early bloom (weeks 1–3 of 12/12): EC 1.8–2.2 mS/cm. The hormonal flip increases demand for phosphorus and potassium.
- Peak bloom (weeks 4–6): EC 2.0–2.4 mS/cm. The highest point of the cycle; push slowly and read your runoff.
- Late bloom (week 7+): EC 1.6–1.8 mS/cm. The plant starts drawing from internal reserves; don't push it.
- Final flush (7–14 days before harvest): EC equal to plain water, no nutrients added. The goal is to clear accumulated salts from the substrate.
How do you calculate your actual dose?
The process has three steps. First, measure the EC of your base water before adding anything — that's your starting EC. Second, identify the target EC for your current stage from the table above. Third, the difference between the two — target EC minus base water EC — is the EC your nutrients need to contribute.
That delta is what the Helix dose calculator converts into milliliters per liter for each product in the line, already calibrated against the real concentrations in the formulas. You don't have to do the math by hand: enter your base water EC, select your stage, and the calculator gives you mL/L per product. The result is a starting point, not a number carved in stone — fine-tune based on how the plant responds visually.
How do you adjust for your water and substrate?
Source water varies a lot: from nearly RO-pure in some regions to EC 0.6–0.8 mS/cm in hard water areas. With hard water, your margin to add nutrients before crossing the EC target is smaller, and the ionic makeup of the water (calcium, magnesium, bicarbonates) can interact with your nutrient formula. Always measure the EC and pH of your base water before mixing your solution.
- Soil: high buffering capacity; pH drifts less but corrections take longer to reach the roots. Raise EC in small steps and give it 2–3 waterings to see the effect.
- Coco: an inert medium with no reserves of its own — what you feed is what the plant gets. Runoff EC tells you in real time whether the concentration at the root zone matches what you mixed. Aim for runoff EC about 10–20% higher than your feed EC.
- Hydro (DWC, NFT, etc.): the solution is in direct contact with the roots. Corrections are immediate, but so are mistakes. Adjust in small increments (0.1–0.2 mS/cm at a time) and check the reservoir every 24–48 hours.
How do you know if you're overfeeding?
Symptoms of excess nutrients (salt toxicity) show up before classic deficiency signs appear. Early warning signs are: leaf tip burn starting at the tips and apex, leaf edges that curl or taco downward, and dark green foliage — especially when nitrogen is running high.
If you're seeing burnt tips, the first thing to check is the EC of your feed solution and — if you're in coco or hydro — the EC of your runoff. A large gap between feed EC and runoff EC signals salt buildup in the substrate: in that case, drop your feed EC and increase your runoff percentage to flush the excess. The burnt tips guide (/guias/puntas-quemadas-bordes-marrones) covers that in detail. The rule of thumb: raise EC by no more than 0.2 mS/cm per week; never jump from EC 1.2 to EC 2.0 in a single feeding.
