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Calculate aquarium water volume in gallons and liters for rectangular, bow-front, cylinder, and corner tanks including substrate and displacement.
Calculate CO2 injection rate for planted aquariums from tank volume, target pH, KH carbonate hardness, and bubble rate for stable dissolved CO2.
Check tropical fish compatibility for community tanks by temperament, tank size, water parameters, and schooling needs before adding new species.
Low-light plants (Anubias, Java fern): 15–30 PAR. Medium (Cryptocoryne, Bacopa): 30–50 PAR. High-light carpeting plants (HC, Monte Carlo): 50–80+ PAR at substrate level.
Target PAR at substrate = Plant category minimum to maximumLight intensity decreases with water depth and clarity. Expect 30–50% PAR loss at 18 inches depth depending on fixture efficiency and water clarity.
PAR at depth ≈ PAR at surface × (1 − depth loss factor)Standard photoperiod is 6–8 hours for planted tanks. LED wattage needed depends on fixture PAR efficiency — modern LEDs deliver 2–4× the PAR per watt of old T5 fluorescents.
Daily light integral (DLI) = PAR × photoperiod hours × 0.0036 (mol/m²/day)Updated: July 2026
12-inch depth, Anubias and Java fern at 20–30 PAR. A 20W LED fixture rated 40 PAR at 12 inches provides adequate light at 7-hour photoperiod without CO2.
16-inch depth, Monte Carlo needs 60+ PAR at substrate. A 60W dimmable LED with 80 PAR at 12 inches delivers ~50 PAR at substrate — supplement or raise light for 60+ PAR.
21-inch depth loses significant PAR. Medium-light stems need 40 PAR at substrate. High-output pendant or multiple strip LEDs may be needed instead of a single low-profile fixture.
The old 2–3 watts/gallon rule applied to T5 fluorescents. Modern LEDs produce 2–4× more PAR per watt. A 30W LED may outperform a 65W T5 — use PAR ratings instead.
Extended photoperiods cause algae, not faster plant growth. If plants are stunted at 8 hours with adequate PAR, the issue is nutrients or CO2, not insufficient light duration.
Light intensity drives plant growth and algae balance in planted tanks. This calculator estimates required PAR (photosynthetically active radiation) and wattage from tank depth, plant category (low, medium, high light), and photoperiod duration.