Plants, light and carbon
Light is the accelerator. It is not the food, and buying more of it is the most expensive way to make a problem worse.
Six corrections here, and one of them is a claim this site repeated before tracing it. The plant chemistry in depth is on the chemistry page and the species detail on find a plant.
Correction 17
"My plants are growing badly, so they need more light." Backwards, and it is the expensive one.
- Commonly said
- Poor growth means insufficient light. Buy a stronger fixture, or run the one you have for longer.
- What the evidence shows
- Light sets the rate at which everything else is consumed. If carbon or a nutrient is limiting, more light only widens the gap, and algae grow into the gap. The carbon side is measurable: across fourteen submerged species, underwater photosynthesis rose on average threefold when carbon supply went from ambient to saturating1, which is the size of the thing light cannot substitute for.
- What to do instead
- Change one variable and wait a month. Six to eight hours is the normal starting photoperiod: start at eight if unsure, six if you have algae, and increase only after a month of stability. That is hobby convention and we could find no measurement study behind it, so it is marked as convention rather than dressed up.
- Why the common version exists
- Light is the one input you can buy in a shop, and it is the one a shop can sell you. Carbon and patience are not on the shelf. There is no conspiracy in that; it is what a shop is.
Correction 18
"Aquatic plants can only use CO2, not bicarbonate." Wrong for about half of them.
- Commonly said
- Without injected carbon dioxide the plants have no carbon, which is why hard water tanks fail.
- What the evidence shows
- Bicarbonate use has been demonstrated in 50 percent of 80 tested freshwater flowering plant species. Bicarbonate users can strip 40 to 70 percent of the dissolved inorganic carbon out of the water; obligate carbon dioxide users manage 1 to 4 percent1. That is why some plants grow well in hard alkaline uninjected water and others sulk in the same tank. It is a different uptake pathway, not a difficulty rating.
- What to do instead
- In hard water, choose bicarbonate users and the tank runs itself. Vallisneria, Egeria, Elodea, Hygrophila, Ceratophyllum and Potamogeton are all good ones, and Yerevan's carbonate reserve is an asset for them rather than an obstacle.
- Why the common version exists
- The hobby's plant lists are sorted into easy and difficult, which flattens a real physiological split into a single scale. Once you have the wrong axis, every observation confirms it. What difficulty actually measures takes that apart in general.
Correction 19
"The pH and KH table tells you your CO2." Only in a tank with no wood, no soil and no peat.
- Commonly said
- Look up your pH and KH in the table and read off dissolved carbon dioxide. Aim for 30.
- What the evidence shows
- The table assumes all your alkalinity is carbonate and no other acids are present. Alkalinity can come from carbonate, bicarbonate, borate, phosphate or hydroxide, so the measurement does not indicate the presence of any one of them2, and a planted tank also makes tannic, humic and uric acids that lower pH with no carbon dioxide involved. In a tank with driftwood, aqua soil or peat the table will overstate your carbon dioxide, sometimes badly.
- What to do instead
- Use the pH drop method, which compares the same water with itself and does not care what your alkalinity is made of. Degas overnight with vigorous aeration and measure pH, then measure with the gas running. A drop of one full pH unit is a tenfold rise in dissolved carbon dioxide2.
- Why the common version exists
- The table is correct arithmetic on a stated assumption, and the assumption holds in a bare injected tank with inert substrate, which is exactly the kind of tank the people who published it were running.
Correction 20
"30 ppm of CO2 is completely safe." Too confident, and the cost is invisible rather than absent.
- Commonly said
- Thirty parts per million is the target and it is entirely safe for fish. Everybody runs it.
- What the evidence shows
- Atlantic salmon post-smolts held twelve weeks showed low mortality at every level from 5 to 40 mg/L, but significantly lower final weight at 12 mg/L and above, with growth declining as carbon dioxide rose3. Rainbow trout held six months at 24 mg/L against 8 mg/L showed survival above 97 percent in both groups and no growth difference4. The accurate statement is that 30 mg/L is a manageable load for healthy tropical fish and that its cost, if any, does not show up as a death.
- What to do instead
- Worry about oxygen instead, because almost every carbon dioxide death happens at night, when the plants consume oxygen rather than making it and the gas keeps arriving. Solenoid on a timer, off an hour before the light, surface agitation overnight.
- Why the common version exists
- Because at 30 mg/L nothing visibly happens, and the hobby's only instrument for safety is whether anything died. A growth effect measured in salmon over twelve weeks is not something a keeper could ever detect.
Correction 21
"Liquid carbon is a cheaper substitute for injection." Its manufacturer does not say that.
- Commonly said
- Dose liquid carbon daily and you get the benefits of injected carbon dioxide without the cylinder. It also clears algae.
- What the evidence shows
- The manufacturer of the best known product rates its effectiveness at 6 to 7 against injection at 10, and states plainly that it is not produced or marketed as an algicide5. The chemistry is a glutaraldehyde relative, which is a known disinfectant, and that is the simplest explanation for what users actually report: spot dosing kills black brush algae and nearby plants are damaged at high dose. A carbon fertiliser would not behave like that.
- What to do instead
- Use it for what it reliably does, which is targeted algae control, and understand that this is off label. Do not plan a high light tank around it. It harms Vallisneria, some mosses and Riccia.
- Why the common version exists
- It does something, immediately and visibly, and the visible thing is algae dying. Attributing that to carbon is a reasonable guess from the label, and the label is a fertiliser label.
Correction 22
"Root tabs feed the plants." For most of what is in a planted tank, the roots are not the mouth.
- Commonly said
- Push root tabs into the substrate and your plants are fed. Rich substrate is the foundation of a planted tank.
- What the evidence shows
- It depends entirely on the plant, and the split is measurable. In a split chamber experiment on rooted submerged plants, the root route supplied 98 percent of photosynthesis in a true isoetid and 75 percent in another, but only 3 percent in the measured stem plant6, and epiphytes have no sediment contact at all so the mechanism cannot apply to them. The direction runs against fast growth too: across fifteen submersed plant communities in acidic lakes, the relative importance of sediment carbon using species was significantly negatively correlated with free carbon dioxide in the water column7. Root carbon use is a low carbon specialism with a growth rate cost, which is the opposite of what a hobbyist quoting it is hoping for.
- What to do instead
- Root tabs for rosette plants with real root systems: swords, crypts, Vallisneria, Sagittaria, bulb plants. Water column dosing for stem plants, mosses, floaters and epiphytes. Both, in a tank that has both. Find a plant records which route each species feeds by.
- Why the common version exists
- Because dirted tanks demonstrably work, and the obvious explanation for a tank with rich soil growing well is that the soil is feeding the roots. The likelier explanation is that a dirted tank is a well fed tank with a slow release nutrient bank and usually a low light one, so demand is matched to supply by turning demand down rather than supply up.
Correction 23 · a claim we repeated ourselves
"Ammonium in the water switches the roots off by 77 percent." It is a marine seagrass result and there is no freshwater equivalent.
- Commonly said
- Aquatic plants prefer to take ammonium in through their leaves, and putting nitrogen in the substrate works against the plant's own preference. The figure quoted is 77 percent suppression of root uptake.
- What the evidence shows
- The direction is probably right and the number belongs to another system. The 77 percent figure traces to a 1982 split chamber study in which ammonium added to the leaf compartment cut root uptake by 77 percent while ammonium at the roots did not reduce leaf uptake at all8. The organism is Zostera marina, eelgrass, a marine seagrass and not a freshwater aquarium plant The widely circulated version reaches the hobby through a secondary summary that cites it correctly and is then quoted without the species9. We looked for an equivalent measurement in any freshwater aquatic plant and found none. The 1982 paper is paywalled and we have read only its bibliographic record, which is stated here rather than hidden.
- What to do instead
- Treat the direction as suggestive and the number as belonging to another system. It is not a reason to stop using root tabs on rosette plants, which is what correction 22 is actually about. It is a reason not to quote 77 percent.
- Why the common version exists
- Nobody fabricated anything. A correctly cited figure in a reference list traveled one hop into general use and lost its species on the way, which is the single commonest failure mode in this hobby's information and is why this page exists. We repeated it too, and the entry for that is in what we got wrong.
The room, the floor and the air
Four of these change what you buy, and one of them is that you may not need an air pump.
A tank is a slab of water with one open face, standing on a floor, in a city 1,100 meters above the sea. Each of those three facts overturns something the hobby says with confidence. The full derivations are on the physics page.
Correction 24 · the one that saves money
Gas exchange depends on depth and not at all on volume, so a shallow tank may need no air pump.
- Commonly said
- Bigger tanks are more stable, so they hold their oxygen better. Every tank needs an air pump, and a bigger tank needs a bigger one.
- What the evidence shows
- Oxygen enters across the air to water interface and nowhere else, so supply is proportional to area while the thing being supplied is proportional to volume. Write the standard two-film expression, divide by volume to turn mass into concentration, and notice that volume over area is the definition of mean depth. The volume cancels. The recovery rate is inversely proportional to mean depth, so a 20 liter tank and a 400 liter tank of the same depth re-oxygenate at exactly the same rate, and a container twice as deep recovers half as fast whatever its volume10. Two shapes holding the same 200 liters make the point: 1.00 by 0.80 by 0.25 m has a surface of 0.80 m2 and a mean depth of 0.25 m; 0.50 by 0.40 by 1.00 m has 0.20 m2 and a mean depth of 1.00 m; at the same transfer velocity the shallow one resupplies four times as fast per liter10. Same water, same cost.
- What to do instead
- Choose the shape before you choose the equipment. If the container's time constant is shorter than a night, it refills its own oxygen before dawn and needs no pump, which is why the wide tub and the pond jar work at all and why a barrel does not. Use mean depth, not maximum depth: a tub with a deep middle and shallow shelves has a mean well below its deepest point.
- Why the common version exists
- Big tanks really are more stable, and the observation is sound. It is thermal mass and dilution that make them so, and those have been quietly relabelled as gas exchange. Everything in the received version is true except the mechanism.
Correction 25
Every oxygen table in the hobby is wrong in Yerevan, by about 13 percent10.
- Commonly said
- At 25 degrees water holds about 8.2 mg/L of oxygen. The table is in every book and on every forum.
- What the evidence shows
- Those tables are computed at sea level pressure and Armenia is not at sea level. Correcting the standard freshwater solubility measurement11 for Yerevan Arabkir's station height of 1113 m and pressure of 887 hPa12 gives 6.58 mg/L at 30 degrees rather than 7.56, a shortfall of 13.0 percent, and 12.5 percent at 0 degrees10. Gyumri at 1513 m and 846 hPa loses about 17 percent; Meghri at 627 m and 940 hPa, the lowest station in the country, loses only 7.5 percent1210. It applies on exactly the days when the margin is thinnest, because the same warmth that lowers supply raises demand.
- What to do instead
- Stock at the July temperature and at your own altitude, not at an annual mean and not at sea level. Meghri is the hottest place in Armenia and its lower altitude partly offsets that, which is the kind of thing only a corrected table tells you.
- Why the common version exists
- Nobody writing aquarium books lives at 1,100 meters. The correction is standard in limnology and aquaculture and simply never crossed into the hobby, because near sea level it changes the result by only one or two percent.
Correction 26
"Your floor cannot take an aquarium." Pressure per square meter does not scale with tank size.
- Commonly said
- The residential floor limit is 1.5 kPa and your tank is four times it, so the floor will fail. Site it against a load bearing wall.
- What the evidence shows
- Pressure on the floor is mass over footprint, which is dimensionally a density times a height, and tanks all have roughly the same height. So every tank from 60 to 500 liters lands between 5.3 and 7.0 kPa, while total mass goes from 97 kg to 766 kg, a factor of eight10. For comparison, a filled bath is 2.1 kPa, a washing machine 2.2, a full bookcase 7.3, an adult standing on both feet 21, and a refrigerator on four small feet 8810. The 1.5 kPa figure is the Soviet residential live load Armenia inherited13 and Eurocode recommends 2.0 kPa for the same category14, but both are uniformly distributed loads, not crushing limits, and taken at face value they condemn a 60 liter tank that nobody worries about. That is the tell. A slab fails in bending, not in crushing. The real test is the bending moment in the member spanning between the bearing walls, and it depends enormously on where along the span the load sits: at a 3.2 m span a 240 liter tank causes 77 percent of the design live load moment at mid span and 39 percent at 15 percent of the span from the wall10.
- What to do instead
- Stop comparing pressures and start thinking about position. Near a wall is dramatically better than in the middle of a room, and it is a free choice. Run across the joists rather than along one. Nothing here is engineering advice for a specific building, and a 350 liter tank at mid span is worth asking somebody about. The siting checklist, including the electrical side, is on the planning page.
- Why the common version exists
- Somebody read a real number out of a real code and compared it to a real pressure, and the two numbers are not comparable. The instinct behind it is sound: a big tank is a serious load and people are right to hesitate. The arithmetic just answers a different question.
Correction 27
"There is far more CO2 in air than in water." The ratio is about 1.1 to 1.2.
- Commonly said
- Air is 420 parts per million and tank water holds 0.6 mg/L, so an emersed leaf has hundreds of times more carbon available. Injection closes the gap.
- What the evidence shows
- The comparison is invalid at the first step, because it puts a mixing ratio next to a mass concentration. Convert both to the same unit, using the ideal gas law on one side and Henry's law with its temperature coefficient on the other15, and the illusion disappears: at 420 ppm the air holds 17.5 micromoles per liter at 20 degrees against 16.1 dissolved, a ratio of 1.08, and 17.2 against 14.0 at 25 degrees, a ratio of 1.2216. Station pressure cancels out of the ratio entirely. The conclusion was right and the reason was wrong, and the wrong reason matters, because it makes people believe injection closes the gap. The real difference is transport: the diffusion coefficient of carbon dioxide is about 1.6 by 10^-5 m2/s in air and about 1.9 by 10^-9 m2/s in water, a ratio near 10,00017. The consequence is the diffusive boundary layer, the still film clinging to a submerged leaf, measured at 90 percent of the total resistance to carbon fixation in four submerged freshwater macrophytes1.
- What to do instead
- Buy flow before you buy more gas. Moving water thins the boundary layer, which is the resistance that actually limits the leaf, and it is the cheapest thing on the list. Injection is still transformative, because going from 0.6 to 25 mg/L is a roughly fortyfold rise in the gradient driving diffusion across that film16, but it moves a long way without closing a gap of four orders of magnitude. The altitude penalty applies here too: at 887 hPa a Yerevan tank at air equilibrium holds about 0.54 mg/L at 25 degrees rather than 0.6216.
- Why the common version exists
- It gets the right answer, which protects it from being checked. And it is a unit error of a kind that is genuinely easy to make: 420 ppm and 0.6 mg/L look like numbers that can be divided.
Correction 28
"Measure your light with a lux meter, or with the app on your phone."
- Commonly said
- Take a lux reading at the substrate and divide by a conversion factor to get the number plants care about.
- What the evidence shows
- The lumen is defined against human eye sensitivity, which peaks in the green at 555 nm, and chlorophyll absorbs strongly in blue and red and comparatively poorly in green. So the ratio between lux and photon flux depends entirely on the lamp's spectrum, and the published conversion divisors range from about 50 for incandescent to about 82 for high pressure sodium. A 2023 review states the conclusion directly: photometric quantities are incorrect for describing lighting for photosynthetic organisms, and luxmeters should be avoided18. The inverse square law is the second half of the same problem: it applies to a point source, and a 90 cm tube is not one.
- What to do instead
- Name your light source before converting anything, which is what our light tool requires and why it publishes no single divisor. Report light at the substrate, in the center and at the corners, with the depth stated. A fixture's headline number means nothing without both.
- Why the common version exists
- A lux meter is in every phone and a quantum sensor costs more than most people's tank. A rough number felt better than no number, and for a while it was the only number available.
Outdoors in July
The outdoor pond literature is written for northern Europe, and one of its habits is dangerous here.
Everything published about garden ponds and tub gardens comes from Britain, Germany, the Netherlands and the northern United States, where the summer problem is getting a container warm enough. Yerevan has 82 days a year above 30 degrees, Armavir 90 and Meghri 9112. Nothing in that literature is calibrated for it. The builds are on easy setups.
Correction 29
"Choose a dark container." A dark barrel in the Armenian sun reaches 42.6 degrees19.
- Commonly said
- Pick a dark container. It looks like water, it hides algae, and it warms the pond earlier in the season.
- What the evidence shows
- A small dark container in the open is a solar collector on its walls and sheds heat only through its top. It collects roughly 1.8 times the solar load per liter of a wide flat pond, which is a mean temperature about 6 degrees higher, at 33.3, before any daily swing is added19. Peak July water temperature in the Ararat valley, taken as the mean plus half the daily swing: a 0.30 m light tub with no shade reaches 30.2 degrees, the same tub half shaded 24.1, and a 0.30 m dark barrel with no shade 38.8. A dark barrel 0.20 m deep in a heat spell with a daily mean air temperature of 31 reaches 42.619. The black plastic barrel is the cheapest and most available container in Armenia and it is lethal in the sun. Around 40 degrees is above the survivable range of every animal this hub will recommend.
- What to do instead
- White, pale grey or pale beige, opaque, and shaded. Shade is worth more than depth and the physics says so: going from 0.20 m to 0.60 m of depth in an unshaded light tub buys 3.1 degrees, while going from no shade to half shade at a fixed 0.30 m buys 6.119, and depth costs oxygen while shade does not. Do not overshoot: above roughly 60 percent shade the plants stop growing well19, and the plants are the nitrogen removal. Half shade concentrated between eleven and five, east facing against a wall that blocks the afternoon, is the ideal Armenian siting and it costs nothing to choose.
- Why the common version exists
- Two true things, one of them ours. Opaque genuinely does beat translucent, because algae grow through a translucent wall, and that is easy to read as an argument for dark. And in northern Europe a dark container warming faster is a feature, which is why the advice was written. Both are correct where they were written. Neither survives an Ararat valley July.
Correction 30
"Armenian summers make outdoor keeping impossible." The dryness does most of the work for you.
- Commonly said
- It gets to 40 degrees here, so an outdoor tub will cook. Do not bother.
- What the evidence shows
- The first result of the surface energy balance is a pleasant surprise. An open, light coloured, wide water surface in Yerevan in July sits at about 27.1 degrees, only about 1.5 degrees above the mean air temperature19. Not 35. The reason is dryness: the July vapour pressure in Yerevan is 16.6 hPa and the wet bulb temperature about 18 degrees1219, so evaporative cooling removes most of the solar load. Armenia's low summer humidity is the outdoor keeper's largest single advantage and nobody frames it that way.
- What to do instead
- Build the tub. Two conditions carry the number and both are load bearing: the container must be topped up, so evaporation can continue, and the surface must be open rather than completely blanketed by a floating mat. A container that dries out or is fully covered loses the cooling that produced the figure.
- Why the common version exists
- Because 40 degrees of air is a real number and it is frightening, and the intuition that water follows air is close enough to right in a humid climate. In a dry one the wet bulb is a long way below the dry bulb and the water tracks the wet bulb.
- Pedersen, O., Colmer, T.D. and Sand-Jensen, K. (2013). Underwater photosynthesis of submerged plants: recent advances and methods. Frontiers in Plant Science 4: 140. Open access. The diffusive boundary layer, the 90 percent of total resistance figure, the average threefold rise from ambient to saturating carbon, and the 50 percent of 80 species bicarbonate result. DOI 10.3389/fpls.2013.00140 open access
- Morin, G. Understanding the General Chemistry of the Planted Aquarium. Seachem Laboratories. The equilibrium constants, the statement that an alkalinity measurement does not indicate the presence of any one compound, and the pH drop method. PDF
- Mota, V.C., Nilsen, T.O., Gerwins, J., Gallo, M., Ytteborg, E. and others (2019). The effects of carbon dioxide on growth performance, welfare and health of Atlantic salmon post-smolt in recirculating aquaculture systems. Aquaculture 498: 578 to 586. DOI 10.1016/j.aquaculture.2018.08.075
- Good, C., Davidson, J., Welsh, C., Snekvik, K. and Summerfelt, S.T. (2010). The effects of carbon dioxide on performance and histopathology of rainbow trout in water recirculation aquaculture systems. Aquacultural Engineering 42(2): 51 to 56. DOI 10.1016/j.aquaeng.2009.11.001
- Flourish Excel product page. Seachem Laboratories. The manufacturer's own 6 to 7 against 10 effectiveness rating, and its statement that the product is not produced or marketed as an algicide. seachem.com/flourish-excel.php
- Winkel, A. and Borum, J. (2009). Use of sediment CO2 by submersed rooted plants. Annals of Botany 103(7): 1015 to 1023. Open access. The split chamber percentages, 98 percent of photosynthesis from the root route in a true isoetid and 3 percent in the measured stem plant, and the shoot to root area ratios. DOI 10.1093/aob/mcp036 open access
- Titus, J.E. and Pagano, A.M. (2017). Fifteen submersed macrophyte communities in acidic Adirondack lakes, with free CO2 measured in both the water column and the pore water. The negative correlation between the relative importance of sediment carbon users and water column carbon. cited through the primary literature record
- Thursby, G.B. and Harlin, M.M. (1982). Leaf-root interaction in the uptake of ammonia by Zostera marina. Marine Biology 72(2): 109 to 112. Paywalled. The split chamber result: ammonium in the leaf compartment cut root uptake by 77 percent, ammonium at the roots did not reduce leaf uptake at all. Zostera marina is a marine seagrass. bibliographic record only; full text not obtained and no DOI asserted here
- Walstad, D. (2017, updated 2023). Nitrogen Uptake by Aquatic Plants. Free PDF, carrying its own reference list to the primary literature. Cited here only as the route by which the eelgrass figure in source 25 reaches the hobby. The figure is not her measurement, her citation of it is correct, and it loses its species one hop downstream. dianawalstad.com secondary; the primary is source 25
- Our own arithmetic on gas exchange, altitude and structure. Not a published source. The two film expression divided by volume to give the depth form, the time constants and the two shape comparison at 200 litres. The barometric correction applied to source 33 using the vapour pressures and station pressures in source 36, giving the 12.5 to 13.0 percent Yerevan shortfall, 17 percent for Gyumri and 7.5 percent for Meghri. The mass and floor pressure table, the household object comparisons, and the bending moments at mid span and at 15 percent of the span from the wall, against the design live load moments computed from sources 31 and 32 at a 3.2 m span. calculated, repeatable, unverified by a third party
- Benson, B.B. and Krause, D. (1984). The concentration and isotopic fractionation of oxygen dissolved in freshwater and seawater in equilibrium with the atmosphere. Limnology and Oceanography 29(3): 620 to 632. The primary measurement behind the freshwater oxygen solubility table that the standard handbooks reprint, and the sea level column of the altitude comparison. DOI 10.4319/lo.1984.29.3.0620
- Armenian hydrometeorological service, WMO Climate Normals 1991 to 2020, as submitted to WMO and archived by NOAA NCEI, Region VI Armenia. Station heights, station pressures, monthly means and vapour pressures. Yerevan Arabkir at 1113 m and 887 hPa, Gyumri at 1513 m and 846 hPa, Meghri at 627 m and 940 hPa, the July vapour pressure of 16.6 hPa, and the 82, 90 and 91 days a year above 30 degrees for Yerevan, Armavir and Meghri. primary normals public; the derived station pressures and wet bulb figures are ours
- SNiP 2.01.07-85*, Nagruzki i vozdeystviya (Loads and actions), Table 3. The Soviet residential floor live load of 1.5 kPa, inherited by Armenia. the exact clause number and the currently binding Armenian instrument were not retrieved
- EN 1991-1-1:2002, Eurocode 1: Actions on structures, Part 1-1, Table 6.2, Category A. The 2.0 kPa recommended residential live load. clause numbers not independently verified
- Sander, R. (2015). Compilation of Henry's law constants (version 4.0) for water as solvent. Atmospheric Chemistry and Physics 15(8): 4399 to 4981. Open access. The solubility constant for CO2 and its temperature dependence behind every Henry's law figure here. DOI 10.5194/acp-15-4399-2015 open access
- Our own arithmetic on the carbonate and carbon dioxide systems. Not a published source. The calcite ceiling table, solved as the standard calcite-carbonate equilibrium system at 25 degrees C for a fixed dissolved CO2 with charge balance 2[Ca2+] = [HCO3-], using the constants in sources 1 and 2, activity corrections ignored. The uninjected row is solved at 420 ppm, which is 0.63 mg/L dissolved at 25 degrees, and returns 19.4 mg/L calcium, pH 8.2 and 2.7 dGH. Also the cube root sensitivity of hardness to CO2, the 250 to 350 times seawater to river sulfate ratio from source 1, and the air against water molar table computed by the ideal gas law and Henry's law from source 30 at sea level and at 887 hPa, including the 12.5 percent altitude reduction. calculated, repeatable, unverified by a third party
- Jahne, B., Heinz, G. and Dietrich, W. (1987). Measurement of the diffusion coefficients of sparingly soluble gases in water. Journal of Geophysical Research: Oceans 92(C10): 10767 to 10776. The measured diffusion coefficient of CO2 in water behind the four orders of magnitude. DOI 10.1029/JC092iC10p10767
- Walter, A. and Schobel, H. (2023). Shed light on photosynthetic organisms: a physical perspective to correct light measurements. Photosynthesis Research 156(3): 325 to 336. The statement that photometric quantities are incorrect for describing lighting for photosynthetic organisms and that luxmeters should be avoided. DOI 10.1007/s11120-023-01001-5
- Our own surface energy balance for outdoor containers. Not a published source. A steady state balance of solar gain, longwave exchange, sensible heat and evaporation, run at the Ararat valley July normals in source 36, for eight container and shading scenarios. Returns 27.1 degrees for an open wide light surface, 33.3 degrees mean for a small dark container collecting roughly 1.8 times the solar load per litre, and peak figures of 30.2, 31.8, 24.1, 38.8 and 42.6 degrees. The 60 percent shade limit on plant growth is a modelled light threshold, not a measured one. calculated, repeatable, unverified by a third party
Continue
Where to go next.
Find a plant
Measure the light, then filter on the number instead of the word.
Physics
Why volume cancels, what altitude does to oxygen, and the carbon dioxide transport question settled.
Stone, hard water and the filter
The other half of the corrections: stone, hard water and what is actually living in the filter.
Easy setups
The outdoor and unheated setups, written for this country rather than for northern Europe.
The whole plant table
Every plant record with its light and carbon requirement printed, so the folklore can be checked against the table.