Hydroponic Reservoir Size Calculator
Calculate the minimum reservoir volume for your hydroponic system from plant count, growth stage, and system type.
Prevent nutrient fluctuations and dry-out.
Why reservoir size matters in hydroponics:
An undersized reservoir causes rapid pH swings, nutrient concentration spikes, and temperature fluctuations — all of which stress plants. A properly sized reservoir stays stable between changes and gives you a buffer when life gets busy.
General rule of thumb:
Minimum reservoir = Number of plants × Gallons per plant
Gallons per plant by system type:
| System Type | Gallons/Plant | Notes |
|---|---|---|
| Deep Water Culture (DWC) | 3–5 gal | Each bucket IS the reservoir |
| Ebb and Flow (flood/drain) | 1.5–3 gal | Shared reservoir, cycles 3–4×/day |
| NFT (Nutrient Film) | 1–2 gal | Continuous thin film flow |
| Drip system | 1.5–2 gal | Timer-controlled drip emitters |
| Kratky (passive) | 2–3 gal | No pump — jar method |
| Aeroponics | 2–3 gal | Misted roots, high evaporation |
Worked example:
12 tomato plants in an Ebb and Flow system at 2.5 gal/plant:
- Minimum reservoir = 12 × 2.5 = 30 gallons
- Recommended (add 25% buffer): 37.5 gallons → use a 40-gallon tote
Growth stage adjustment:
Mature, large plants (flowering tomatoes, peppers) drink 1–2 gallons per day each in hot conditions. Seedlings use a fraction of that. Start conservative and watch your water level — if the reservoir drops more than 25% in a day, you need a larger one.
Temperature control:
Larger reservoirs are easier to keep cool. Root zone temperature should stay between 65–72°F (18–22°C). Above 75°F, dissolved oxygen drops and root rot (pythium) risk skyrockets. In warm environments, add a water chiller or use frozen water bottles.
Practical tips:
- Use opaque containers — light promotes algae growth
- Never let the reservoir run dry — exposed roots die within hours
- Top off evaporated water with plain pH-adjusted water, not nutrient solution (this prevents salt buildup)
- Full reservoir changes every 7–14 days keep things stable
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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