Plant Care
- • Climate Control & VPD16
- • Disease & Pest Management14
- • Nutrient Solutions & EC34
- • Plant Health Monitoring7
Inputs
12 parameters · live recalculation on every change
L
10L
200L default
10000L
MS/CM
0mS/cm
0.05mS/cm default
0.5mS/cm
DAYS
0days
7days default
60days
L/DAY
0L/day
2L/day default
50L/day
°C
0°C
20°C default
35°C
Pro Settings — Lab Controls
0
3 default
10
MV/DAY
0mV/day
5mV/day default
50mV/day
MG/L
0mg/L
7mg/L default
15mg/L
Advanced Settings — Deterministic Corrections
0.5
1 default
2
PPM
0ppm
50ppm default
500ppm
PH/DAY
0pH/day
0.1pH/day default
1pH/day
L
0L
20L default
500L
Deterministic model
12 inputs · 10 outputs
Runs 100% in your browser
This is a deterministic model: the same inputs always produce the same outputs, calculated entirely in your browser with nothing sent to any server. It is a planning aid — not a quote, not a dosing instruction, and not a yield forecast. Treat every line as a working estimate and validate it against your own prices and measurements.
It models one system: A hydroponic flush timer that reads your log like a journal: EC current = 1.8 + drift × days + salt term, pH current = 6.0 + pH-drift × days, then the change countdown averages the 0.5 mS/cm EC budget and the 1.0 pH rise budget plus biofilm factor to print days until you change the reservoir. Flush litres, salt buildup, biofilm and pathogen risk, the ORP decay line, and a green—yellow—red safety band keep the schedule honest for the reservoir you actually run.
What the Reservoir Change Timer — EC Drift & Flush Schedule Blueprint returns
The engine computes 10 outputs from your 12 inputs. The headline number is Days Until Change (days), alongside Current EC, Salt Buildup, Current pH. Every output updates live as you change a parameter.
What it does not do
Outputs depend on the inputs and assumptions shown here. Confirm relevant measurements and local conditions before acting.
STEP 01
Log the reservoir: volume, days since the last complete change, and the EC drift per day your meter actually records.
STEP 02
Model the batch EC: fresh 1.8 + drift × days, plus the small salt term accumulation ÷ 1000 × 0.02 × days ÷ biofilm — drift dominates, salt stays a quiet second order.
STEP 03
Model the pH line: fresh 6.0 plus pH-drift × days — the 5.5–6.5 band the archived journal logged drifts out predictably.
STEP 04
Count down the change: average the 0.5 mS/cm EC budget and the 1.0 pH rise against what is already used, then add the biofilm factor so a slime-prone room changes earlier.
STEP 05
Size the flush: 0.2 × reservoir plus 0.5 × salt buildup, trimming what your top-up habit already cycled, and watch the biofilm composite and the ORP decay line.
STEP 06
Close the decision: the green (>7 days) yellow (3–7) red (<3, biofilm >7, pathogen >6, ORP <400) band and a schedule cadence for the grow.
EC_{now} = 1.8 + \delta \cdot t + \frac{S_{acc}}{1000} \cdot 0.02 \cdot \frac{t}{f_{bf}}
Current EC — fresh baseline plus drift and salt concentration
pH_{now} = 6.0 + \delta_{pH} \cdot t
Current pH — fresh baseline plus upward drift
S = \frac{S_{acc} \cdot t}{f_{bf}} + U \cdot t \cdot 0.1
Salt buildup — concentration plus uptake
D = \frac{1}{2}\left(\frac{0.5 - \Delta EC}{\delta} + \frac{1.0 - \Delta pH}{\delta_{pH}}\right) + f_{bf}
Countdown — averaged EC and pH budgets plus biofilm
V_{flush} = 0.2 \cdot V + 0.5 \cdot S - V_{topup}
Flush volume — drain-and-refill sized to the log
R = 0.1 \cdot t \cdot f_{bf} + 0.05 \cdot T + 0.3 \cdot P
Biofilm risk composite — age, heat and pathogen pressure
ORP = 650 - \delta_{orp} \cdot t
ORP decay — the redox line the meter should read
\text{green } D > 7,\ \text{yellow } 3 \le D \le 7,\ \text{red } D < 3 \,|\, R > 7 \,|\, P > 6 \,|\, ORP < 400
Safety bands — change timing, biofilm, pathogen and ORP
The engine grows EC off a fresh 1.8 mS/cm and pH off a fresh 6.0 baseline, with the EC ceiling set 0.5 mS/cm above it and the pH ceiling 1.0 above it — the actionable-drift bands the archived journal flagged.
Honest countdown: a 200 L reservoir drifting 0.05 mS/cm/day sits at ~2.16 mS/cm by day 7 and the tool prints roughly 4 days to change — YELLOW, not a green two-week pass, because half the drift budget is already spent.
Salt buildup S = accumulation × days ÷ biofilm + uptake × days × 0.1: a 50 ppm/day accumulation over 7 days lands ~351 ppm, big enough to matter in the flush but a rounding error in EC while drift dominates.
Biofilm risk runs 0.1 × days × biofilm + 0.05 × temperature + 0.3 × pathogen on a 0–10 scale; a hot slime-prone room crosses "high" well before the EC budget does, and the path bands trip LOW 6.
ORP starts the 650 mV reference from the disinfection provenance and decays per day; below 400 mV the batch is redox-exhausted and trips red on its own — the meter trusts no formula blindly.
Flush volume = 0.2 × reservoir + 0.5 × salt buildup − top-ups cycled, floored at 10% of reservoir: the archived timeline discipline reserved an end-of-cycle drain-and-refill, and water you already topped up counts as partial renewal.
- EC current: EC = 1.8 + drift × days + (accumulation ÷ 1000) × 0.02 × days ÷ biofilm — the archived top-up engine held reservoir EC inside a band and only re-checked after a 0.1 mS/cm drift; the fresh-baseline 1.8 mS/cm model extends that drift discipline into a per-day log.
- pH current: pH = 6.0 + pH-drift × days — the archived grow-journal logged EC and pH drift per batch against the 5.5–6.5 band; the 6.0 fresh baseline is that band mid-point carried straight into the countdown.
- Salt buildup: S = accumulation × days ÷ biofilm + uptake × days × 0.1 — the archived evapotranspiration engines modelled pure-water transpiration concentrating the salts left behind; the uptake arm reproduces that concentration as reservoir ppm.
- Countdown: days = [ (0.5 − EC excess) ÷ drift + (1.0 − pH rise) ÷ pH-drift ] ÷ 2 + biofilm — the change timer averages the 0.5 mS/cm EC budget and the 1.0 pH rise the archived journal called actionable drift, then lets biofilm push the change earlier.
- Flush volume: V = 0.2 × reservoir + 0.5 × salt buildup − top-ups cycled — the archived timeline planners reserved an end-of-cycle flush before harvest; this sizes the same drain-and-refill for your current log and credits the water you already cycled.
- Biofilm, pathogen and ORP: R = 0.1 × days × biofilm + 0.05 × T + 0.3 × pathogen; ORP = 650 − decay × days — the archived water-temp tool tied warm reservoirs to root hypoxia, and the disinfection provenance pinned a 650 mV ORP baseline; both feed the red-edge bands.
This model combines the earlier Reservoir-change-calculator, Water-change-scheduler, Nutrient-flush-timer models.
Q1: How often should I change reservoir water in hydroponics? ▾
There is no fixed calendar: the change day falls where the EC and pH budgets run out. The engine grows EC off a fresh 1.8 mS/cm baseline at your measured drift per day, grows pH off 6.0, then averages how many days are left in the 0.5 mS/cm EC budget and the 1.0 pH budget. A 200 L reservoir drifting 0.05 mS/cm/day starts ~11 days out on a fresh fill and is ~4 days from change by day 7 — a healthy two-week cadence. A warm, slime-prone or previously infected room changes earlier because the biofilm factor and pathogen score advance the date.
Q2: Reservoir change timer calculator: how does it decide when to drain and refill? ▾
The timer averages two independent budgets every time you change an input. First the EC arm: fresh 1.8 mS/cm plus drift × days plus the small salt term, measured against a 0.5 mS/cm ceiling — half the budget is already gone at a 0.05/day drift by day 10. Second the pH arm: fresh 6.0 plus pH-drift × days against a 1.0 rise. Days until change = (budget days EC + budget days pH) ÷ 2 + biofilm factor, clamped to zero. Add biofilm crowding, pathogen pressure, or an ORP read that decays under 400 mV and the change advances into red, no matter what the EC says.
Q3: EC drift calculator: why does EC rise and when is it dangerous? ▾
EC rises for two reasons the tool separates cleanly. Drift: each day plants and evaporation concentrate the existing salts, roughly linear at the per-day mS you log. Salt accumulation: background ppm gain on top of uptake — hard water, residue, recirculating carry-over — enters as accumulation ÷ 1000 × 0.02 × days ÷ biofilm. The engine flags danger not at a raw number but at the budget: 0.5 mS/cm over the 1.8 fresh baseline, plus any red edge from biofilm, pathogen, or ORP. Top-up with pure pH-balanced water, not fresh nutrient, or the EC climbs faster than the schedule assumes.
Q4: When do I flush a hydroponic system? ▾
Flush when the change timer says red — fewer than 3 days in the countdown, biofilm risk over 7, pathogen level high, or ORP under 400 mV — or when you cycle toward harvest and want the salts cleared before the finish. The flush arm sizes the drain-and-refill: 0.2 × reservoir litres plus 0.5 × salt buildup, minus the top-ups you already cycled, floored at 10% of the tank. A 200 L reservoir at 351 ppm salt buildup suggests roughly 215 L through the loop — drain, rinse the roots and lines, refill at fresh 1.8 mS/cm, and the countdown restarts.
Q5: What causes EC and pH drift between reservoir changes? ▾
Drift is the normal chemistry of a closed loop: plants transpire pure water and leave salts, so EC climbs while pH climbs toward 7 as the buffer weakens and nitrification acid is consumed. The tool models EC off drift × days plus a salt term and pH off pH-drift × days from the 6.0 baseline, into the ceilings 0.5 mS/cm and 1.0 above fresh. Fast drift usually means the canopy drinks more than the reservoir is sized for, a failing sensor, or top-ups made with nutrient instead of plain water — the archived journal logged the same drift and corrected with the 5.5–6.5 pH band.
Q6: What ORP should a healthy nutrient reservoir read before I change it? ▾
The engine starts every reservoir at the 650 mV reference from the disinfection provenance and decays it per day at the rate you log — ORP = 650 − decay × days. A fresh 200 L fill reads ~650 mV, and 7 days at 5 mV/day is ~615 mV; anything under 400 mV means the redox balance is exhausted and the band trips red on its own. Biofilm risk and pathogen level follow the same composite — 0.1 × days × biofilm + 0.05 × temperature + 0.3 × pathogen — so a high-mV reading at warm temperatures still advances the change. Trust the strip and the meter together, never one alone.