Hydroponic Reservoir Top-Up Schedule Calculator
Calculate hydroponic reservoir refill and full reset schedule.
Enter system size and plant uptake to get daily top-up volume and weekly EC drift expectations.
Hydroponic Reservoir Maintenance
In an active hydroponic system, plants drink water faster than they consume nutrients. This causes the EC (nutrient concentration) to rise as the reservoir shrinks. Top-up with plain water keeps EC stable; full reset every 1-3 weeks prevents salt buildup.
Daily plant water uptake (typical):
| Plant Stage | Uptake per Plant |
|---|---|
| Seedling (week 1-2) | 0.05-0.1 L/day |
| Veg (week 3-5) | 0.2-0.5 L/day |
| Early flower / bloom | 0.5-1.0 L/day |
| Mid flower (peak) | 1.0-2.5 L/day |
| Late flower / harvest | 0.7-1.5 L/day |
Light hours and temperature multiplier:
- 12-hour photoperiod: 1.0× baseline
- 18-hour photoperiod (veg): 1.4×
- High temps (above 80°F / 27°C): 1.5×
- Low temps (below 65°F / 18°C): 0.7×
Reservoir reset frequency:
| System Size | Reset Frequency |
|---|---|
| Under 5 gal: tight system | Weekly |
| 5-15 gal: standard | Every 1-2 weeks |
| 15-50 gal: large recirculating | Every 2-3 weeks |
| Drain-to-waste systems | No reset needed (no recirculation) |
EC drift signals:
- EC rising 0.2+ in 24 hours: too concentrated — top up with plain water
- EC dropping: plants eating more nutrients than water — add full-strength solution
- EC unchanging in heat: probably stagnant, check pump
The 25% rule: Once your reservoir drops below 75% of original volume, top up with water — don’t let it concentrate further. Once you’ve added water equal to 40% of original volume in tops, full reset is due.
Top-up vs. reset:
- Top-up: plain water (or weak solution) to restore volume
- Full reset: drain system, scrub reservoir, refill with fresh nutrients
- Why reset? Salts that plants don’t use accumulate — they crystallize roots and clog drippers
Cleaning between resets:
- Mild bleach (1:100) or H2O2 (1 oz / gallon) for sterilization
- Citric acid for hard-water mineral residue
- Always rinse thoroughly before refilling
Monitoring tools (essential):
- EC/TDS meter (Bluelab, HM Digital): $40-200
- pH meter: $30-100
- Float valve / level sensor: optional but useful for absent owners
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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