CO2 Bubble Rate vs Tank Volume Chart Guide: BPS Targets

Bubble counts are the planted-tank keeper’s blunt instrument for setting CO2 — imprecise, dependent on diffuser type and bubble size, but still the most-used number in the hobby. CO2 bubble rate chart targets give you a starting line, not a finish line, because what actually matters is dissolved ppm at light-on. This guide from Gensou Aquascaping at 5 Everton Park lays out bubble-per-second baselines for tank volumes from 30 to 400 litres, then explains why two tanks at the same BPS can read 15 ppm and 35 ppm.

Why Bubble Counts Are Approximations

A “bubble” from a glass diffuser at 0.6 bar is roughly 4 mm; a bubble from a U-shape inline reactor is invisible because it dissolves before it forms. Bubble size, regulator pressure, and diffuser efficiency all change how much actual CO2 enters the water per visible bubble. Treat the chart below as a starting point and verify with drop-checker colour and pH drop measurements.

Baseline Chart for Glass Diffusers

For ceramic glass diffusers running at 0.5-0.7 bar working pressure: 30L tank — 0.5 BPS. 60L — 1 BPS. 100L — 2 BPS. 150L — 3 BPS. 200L — 4 BPS. 300L — 6 BPS. 400L — 8 BPS. These assume the diffuser sits under flow from a canister filter outlet to maximise dissolution. A ceramic CO2 diffuser in a tank without good cross-flow loses 30-40 per cent efficiency, requiring proportionally higher BPS.

Adjustments for Inline Atomisers

Inline atomisers (post-canister, pre-lily-pipe) dissolve CO2 at 90-95 per cent efficiency versus 60-70 per cent for in-tank glass diffusers. Cut the BPS targets by roughly one-third: 200L tank with inline runs at 2.5-3 BPS instead of 4. The trade-off is more frequent ceramic disc maintenance — clean every 4-6 weeks with citric acid soak to prevent bubble-size drift.

Adjustments for Reactors

Powered CO2 reactors (Cerges, Aquario Neo, custom) dissolve at near 100 per cent. A 200-litre tank with a reactor needs only 2-2.5 BPS to hit 30 ppm. Reactors suit tanks over 250 litres where in-tank diffusers struggle to spread CO2 across the footprint. Smaller tanks see no benefit and pay the noise cost of an extra circulation pump.

The 1.0-1.2 pH Drop Rule

The reliable target is a 1.0-1.2 pH drop from pre-CO2 baseline to peak photoperiod. PUB tap at pH 7.0-7.2 should drop to pH 6.0-6.2 with 30 ppm CO2. Measure with a calibrated pH pen at lights-off (pre-CO2 on) and again at the start of photoperiod hour three (peak). If you hit only 0.6-0.8 pH drop at the chart’s BPS, raise BPS by 30-50 per cent until you hit the target.

Drop Checker Cross-Check

A 4 dKH reference solution drop checker should read lime green at 30 ppm, yellow at 50+ ppm, blue below 15 ppm. The lag is 2-3 hours, so use it as a confirmation tool not a real-time gauge. Check it visually at hour 4 of photoperiod — that is when both the tank and the checker are at steady state. Pick up reference solution and a checker from the CO2 accessories range.

Solenoid Timer and Ramp Strategy

Bubble rate is meaningless without timing. Solenoid on 1-2 hours pre-light, off 1 hour pre-light-off. This builds CO2 to peak by light-on and lets levels fall before lights-out so fish and shrimp do not suffocate at night. Tanks running CO2 24/7 without a solenoid push fish into morning gasping behaviour and waste 60 per cent of the gas.

Singapore Climate Quirks

Tropical 28-30°C tank temperatures hold less dissolved CO2 than the 22-24°C reference temperatures most charts assume. At 28°C, CO2 saturation drops by about 12 per cent versus 22°C, meaning Singapore tanks need 10-15 per cent higher BPS than European hobby tank charts suggest. A tank with a tight-fitting lid reduces gas-off and lets you run leaner CO2 — open-top rimless tanks burn through gas faster.

Working Calibration Sequence

Day 1: set BPS per chart, dose at lights-on through to lights-off. Day 2 morning: measure pH drop. If under 1.0, raise BPS by 25 per cent. Day 3: re-measure. Iterate every two days until pH drop hits 1.0-1.2 stably. Watch fish behaviour — surface gasping at peak photoperiod means CO2 is too high regardless of pH reading. Every regulator and diffuser combination needs its own calibration; the chart only saves you the first three days.

Related Reading

• CO2 Pressure Ramp Schedule Guide
• CO2 30ppm Verification Methods Guide
• CO2 Reactor vs Diffuser Decision Guide
• Aquarium pH Drop Test Guide
• Aquarium Drop Checker Setup Guide