CO2 and light
How dissolved CO2 is estimated, measured and supplied, and what light figures such as PAR, PPFD and grower ratings mean.
CO2 in a planted tank is rarely measured directly; it is inferred from KH and pH or from a drop checker. These guides derive the carbonate-equilibrium formula behind both, show where the estimate breaks (other buffers, measurement error, temperature) and compare it with the shortcut printed on most charts.
The lighting guides define the units growers and lamp makers use and explain what plant data such as "low", "medium" and "high" light demand do and do not tell you.
9 guides
- CO2 from KH and pH: the formula, the chart and where it breaksWhere the KH/pH/CO2 chart comes from, why its factor of 3 differs from the temperature-corrected 3.5, and the conditions under which both estimates fail.
- How a drop checker works, and what its green actually meansA drop checker is a small KH/pH test with its own reference water. The indicator chemistry, what green corresponds to in mg/L at 4 dKH, and its limits.
- How much CO2 is in aquarium water without injection?Henry's law and today's atmospheric CO2 put water in equilibrium with air at about 0.6–0.7 mg/L. The calculation, the temperature effect and what it means.
- Liquid carbon products: what the labels claim and what is establishedWhat Seachem Flourish Excel and Tropica Carbon Nutrition say about themselves, what their pages leave out, and the hazard data PubChem lists for glutaraldehyde.
- PAR, PPFD and DLI: the light units that matter to plantsWhat PAR, PPFD and DLI measure, why lux, lumens and watts do not describe light for photosynthesis, and how to turn a PPFD reading and a photoperiod into a DLI.
- Photoperiod: how many hours a planted tank's light should runWhat growers and retailers recommend for daily lighting hours, how photoperiod and intensity add up to the daily light dose, and when shorter days are advised.
- Pressurized CO2 systems: the parts and what each one doesCylinder, regulator, needle valve, solenoid, bubble counter, check valve and diffuser: what each part does, per manufacturers, plus the gas safety basics.
- Setting CO2 with the pH-drop methodCompare tank water with a degassed sample: each pH unit of difference means ten times the CO2. The arithmetic, what the baseline really is, and its limits.
- What low, medium and high light and CO2 mean in grower plant dataTropica's light and CO2 ratings, the definitions behind them, the three different CO2 bands on its own pages, and how Aquasabi's categories line up.