Algae

What it models

A bloom is plant mechanics without a position. It has a condition and an energy budget — a reserve, tissue and four nutrient stores — on the vitality model, and its light curve, income, harms, shedding and budget are the plants’, on the plants’ constants and its own traits. It runs at κ = 1: its growth is its reproduction. It has no height or footprint: in their place is a habitat it fills, and spores land in it and join it.

The tank holds two kinds on that one model and one code path. They differ by habitat and traits, and the tank’s conditions pick the winner, with no coded preference.

Kind	Habitat	Size of it	Light it reads	Light taken from	Taken out by
Green water	The water column	The tank’s litres	The column’s mean	Everything below it — itself, the film, each plant by its depth	A water change, by the share changed
Film	The lit surfaces that do not grow: the glass walls, the floor and the hardscape	cm² of them	The walls at the column’s mean, the floor and hardscape at what the canopy leaves, weighted by area	Every leaf, at its coverage	A scrub, off the glass; a bed swap, off the floor

Coverage, 0–100, is the bloom’s tissue over what its full habitat holds at the kind’s tissue density, so a change of habitat moves coverage, not tissue: a piece of hardscape set down thins film’s coverage and keeps its grams. Film’s habitat moves only with the hardscape, never with the planting: the leaves wear its coverage but are not habitat.

Status

Mechanic	Status	Why
Condition and budget	settled	The shared vitality step on the plants’ budget at κ = 1, repair paid from its reserve.
Income	settled	The plants’ three channels, full on a full reserve and full stores.
Growth	settled	Maintenance first, then tissue at the Droop limit through the crowding taper — the share of its habitat still empty — day and night.
Spores	settled	Immigration at a constant rate per kind, built of the water’s CO₂ and nutrients, so an empty tank is never closed to either while its water holds carbon.
Two kinds	settled	Two trait records on one path. Green water is the sprinter: a lit, fed day about doubles it, but it needs richer water. Film is the stayer: a third of the pace, so it takes a week or two to show, but efficient on lean water.
Habitats	settled	A water change carries green water out with the water; a lifted piece of hardscape takes its share of the film, and a swapped bed the floor’s, arriving bare.
Nutrients	settled	Its own Q_min and Q_max, filled from the water alone in one draw with every plant: no feeder is served before another.
Nitrogen form	settled	Ammonia first and nitrate for the rest, on each kind’s affinities: film takes nitrate about as readily as a plant.
Carbon and oxygen	settled	The plants’ photosynthesis and burn on one CO₂ stock, its tissue rated at the plants’ relation and run at its growth rate; its spores draw the CO₂ they are built of beside every fixer.
Allelopathy	settled	Thriving plant leaf per litre lowers every kind’s assimilation ceiling, with no threshold — a stress on its budget, not a harm, standing for every way a planting suppresses algae that the model doesn’t resolve.
Shedding and death	settled	The plants’ shape; condition 0 kills what is left. Tissue returns as waste at Q_min, a die-back’s stores with it; a die-back that showed is logged.
Scrubbing	scaffolding	Coverage is one figure, so the scrubbed glass refills from the floor and the hardscape at once — see Actions.
Light taken	settled	Light, not damage — Beer–Lambert on its coverage.
Film on the leaves	scaffolding	One coverage over the habitat, worn by every leaf alike: a months-old leaf carries no more than last week’s, so film costs a light-hungry plant more than a slow one.
Calibration	scaffolding	First-pass, not fitted. Film’s affinities and quotas are culture and periphyton figures, its K and Fe borrowed from green water’s; green water’s 25 ppm nitrate half-saturation is fitted from whole-tank runs; no store’s fill time is published.

How it works

What feeds it and what harms it

Channel	Side	Reads
CO₂	income	Monod on dissolved CO₂ at its co2HalfSaturation — far under any plant’s, since algae take bicarbonate too
Temperature · pH	income, then harm	The plants’ band helpers on its own bands: comfort peaks mid-band, damage starts at the edge
Starvation	harm	The share of the hour’s upkeep its budget left unpaid: a bloom burns fast, so it starves fast
Nutrient deficiency	harm	Its Droop limit under droopEdge of its full stores’

Every harm is hardened by the kind’s hardiness; income, earned on its reserve and stores, runs through the night.

The budget

A bloom runs the plants’ budget: uptake fills its stores, photosynthesis its reserve, and the reserve pays maintenance first and builds tissue with the rest, at the Droop limit of its emptiest store. Its room to grow is the share of its habitat still empty, so growth slows as coverage nears 100 and stops there. A full reserve caps what it fixes, so a bloom on spent stores fills with carbon it cannot use.

It lives on its stores after the water runs lean, then fades: green water put at 30 % into an unplanted tank with no nitrogen or phosphorus, the fish unfed and a quarter of the water changed weekly, stands at 36 % after a week, 18 % after a month and 5 % after three.

Allelopathy

Thriving plants’ exudates reach a bloom through its budget: they lower its assimilation ceiling by hyperbolic inhibition on thriving leaf per litre, halving it where allelopathySeverity times that dose is 1. A held-back bloom fixes, draws CO₂ and earns less, and takes no damage. Plants hold green water back twice over: they draw on the same water and cut what it fixes.

Spores

Spores are the bloom’s immigration, asked each hour at sporeRate through the taper. They are built of CO₂, drawn on the bloom’s own curve in the one draw every fixer makes, and at Q_min in the same pooled draw as every store — so water short of carbon or a nutrient builds fewer, and a tank with no CO₂ grows no spores. They land unfed — tissue and stores, no reserve — once the bloom’s losses are taken, joining a standing bloom at its condition. Only an empty bloom, died back or never stood, starts afresh from them at 100.

Light

Each kind reads the mean PAR over its habitat, and takes light by Beer–Lambert on its coverage (Light). Green water joins the water’s extinction in proportion to its coverage, so the column it reads darkens as it thickens — a bloom self-limits — and so does every surface under it: the film on the walls and the floor, and every leaf by the depth above it. Film coats every lit surface at its coverage, leaves included; the glass it coats stands beside the lamp’s path, not in it. Neither kind charges a plant anything: a shaded plant fixes less, and starves only once its reserve can no longer pay.

Gases and nutrients

Its tissue is carbohydrate at its kind’s Q_min. A gram of it is the same rate units a gram of leaf is, run at the kind’s growth rate, so a dense bloom strips CO₂ by day and draws oxygen down by night. Shed and dead tissue goes back as waste, a die-back’s stores with it — so a crashing bloom spikes ammonia as it rots.

Each kind takes its nitrogen as the plants do — ammonia first, nitrate for what ammonia leaves — on its own affinities. A cycled tank’s trace of ammonia and a few ppm of nitrate meet most of film’s need, so a lean tank feeds it. The same water meets less of green water’s, and ammonia rising past the trace — a new tank, an overfed one, a melt — meets most of it. A thinly planted, brightly lit tank can go green even when maintained, on leaner water than a well-planted one keeps clear.

A scrub takes the walls’ share of the film into the water as waste, tissue, reserve and stores. A water change takes its share of the green water out, stores and all.

Blackouts

A dark tank starves a bloom on its reserve, not on the day. From 10 % coverage green water dies back in about two weeks and film a day or two later, and the log says so. Spores keep landing, start the bloom afresh at 100 and starve in turn, so the dust dies back every two weeks while the dark lasts, too thin to show: the keeper sees clear water, a clean glass and no more die-backs. Relit, film is back past 20 % within a month.

Key tunables and traits

The tunables are listed in the reference under Algae and the bloom optics under Optics. The table holds each kind’s traits, defined beside the plant species.

Name	Meaning	Green water	Film
habitat	Where it lives	column	surfaces
growthRate	The pace its tissue fixes and burns at, on the plants’ scale	10	4
hardiness	Scales every harm by 1 − hardiness	0.4	0.4
lowLight	PAR at the bottom of its band: its rated day over a care-sheet day, and Ik at saturationIrradianceFactor × it	6 PAR	6 PAR
nutrientDemand	Its demand tier for potassium and iron, as a plant’s	low	low
Temperature · pH bands	Where comfort peaks and harm starts, at least as wide as every plant’s	12–34 °C · 4.5–9.5	12–34 °C · 4.5–9.5
co2HalfSaturation	CO₂ it fixes at half rate on	0.3 mg/L	0.3 mg/L
ammoniaHalfSaturation	Total ammonia, as NH₃, it meets half its nitrogen need on	0.5 ppm	0.02 ppm
nitrateHalfSaturation	Nitrate it meets half its nitrogen need on	25 ppm	1 ppm
phosphateHalfSaturation	Phosphate it meets half its phosphorus need on	0.2 ppm	0.02 ppm
tissueDensity	Organic matter a full habitat holds	0.54 g/L	0.0045 g/cm²
sporeRate	Coverage that lands an hour, through the taper	0.0002	0.002
quotaMin	Q_min of N · P · K · Fe	25 · 1.5 · 4 · 0.03 mg/g	34 · 1.7 · 4 · 0.03 mg/g
quotaMax	Q_max of the same	100 · 15 · 22 · 0.2 mg/g	80 · 10 · 22 · 0.2 mg/g
storeFillDays	Days an empty store takes to fill from saturating water, at its opening rate	1	2

Seams

Neighbour	Read	Written
Plants	Thriving leaf per litre, and the canopy over the floor, as the hour starts	The light each kind takes from every leaf; a share of every pooled uptake and of the CO₂
Light	The mean PAR over each habitat, and the day of it	Green water’s coverage, in the water’s extinction; film’s, the coat on every leaf
Nitrogen cycle	NH₃ and NO₃, PO₄, K and Fe, as the water holds them	Stores and spores filled, the ammonia from what the colony left; shed, dead and scrubbed tissue in as waste, a die-back’s and a scrub’s stores with it
Water & gases	CO₂, O₂, temperature, pH	CO₂ fixed and O₂ released by day, its spores’ too, burned day and night; KH moved by the form its nitrogen comes in
Equipment	The hardscape’s surface, part of film’s habitat	A swapped bed takes the floor’s share of film; a piece set down thins its coverage, one lifted takes its share
Actions	—	A water change takes its share of the green water out of the tank; a scrub takes the film on the glass, stores and all, into the waste
Alerts & logging	—	Each kind raises its own alert once per crossing of its level; an algae-died entry per die-back of a bloom that showed, naming the kind and stating the coverage it took

Source

src/simulation/algae/ holds the kinds, their traits and habitats, src/simulation/systems/ their vitality and the flora law and budget they share with the plants, and src/simulation/flora/ the pass that runs them beside the plants; src/simulation/config/ holds the allelopathy tunable with the algae’s and the bloom optics with the optics.