CO2 Injection Rate Bubble Counter Guide: BPS Per Litre

Bubbles per second is the most quoted and least reliable metric in the planted hobby, yet it remains the easiest way to set a starting point for CO2 injection. This CO2 injection rate bubble counter guide from Gensou Aquascaping in Singapore gives realistic BPS targets per litre for low-tech and high-tech tanks, then explains why the drop checker is the only honest way to confirm dissolved CO2 is in the right zone. Bubbles count, dissolved gas matters.

Quick Facts

• Low-tech rule of thumb: 1 bubble per second per 50 litres
• High-tech target: 1 bubble per second per 30 litres
• Bubble size varies between counters, so BPS is approximate
• Drop checker confirms 30ppm dissolved CO2 when lime-green
• Yellow drop checker means too much CO2; blue means too little
• Diffuser efficiency changes the maths by 20 to 40 percent
• Always start low, raise gradually over a week

Why BPS Per Litre Is Only a Starting Point

A bubble from a glass JBL counter is roughly half the volume of one from a tall acrylic counter. Two tanks injecting at the same BPS may dissolve very different amounts of gas. Diffuser type matters even more. A ceramic disc near a powerhead intake dissolves perhaps 90 percent of the gas, while the same disc tucked in a corner loses a third of the bubbles to the surface unbroken. Inline reactors approach 100 percent dissolution. Always treat BPS as a setting dial, not a measurement.

Low-Tech Targets

For a low-light planted tank running undemanding species like Anubias, Java fern, Cryptocoryne and easy Echinodorus, aim for around 1 bubble per second for every 50 litres of water volume. A 60 litre flat starts at roughly 1 to 1.5bps. The goal is to raise dissolved CO2 from the natural 2 to 3ppm in PUB tap water up to a stable 15 to 20ppm. This range is enough to push growth without forcing you into daily fertiliser dosing.

High-Tech Targets

For a CO2-injected aquascape with high lighting, full ferts and demanding species like Hemianthus callitrichoides, Rotala wallichii or red Ludwigia, push toward 1 bubble per second per 30 litres. A 90 litre tank lands around 3bps. The goal here is to hold dissolved CO2 at 25 to 30ppm during the photoperiod, which is the sweet spot where carbon stops being the limiting factor and lighting takes over.

Drop Checker Confirmation

A drop checker filled with 4dKH reference solution and bromothymol blue indicator gives a one to two hour delayed reading of dissolved CO2 in the water column. Lime green corresponds to roughly 30ppm, considered the upper safe limit for most fish and shrimp. Yellow-green sits closer to 40ppm and is the warning zone. Pure blue indicates under 10ppm, a sign of leaks, blocked diffuser or insufficient injection.

Place the drop checker on the side of the tank opposite the diffuser, at mid-water. Refresh the solution monthly; old indicator drifts and reads falsely yellow.

Tuning by the Hour

Start CO2 one to two hours before lights on and stop it one hour before lights off. Plants only photosynthesise under light, so injecting overnight wastes gas and risks pH crashes. By the time lights come on, the drop checker should already be showing yellow-green from the head start. Mid-photoperiod it should hold lime green. By lights off it can drift back toward blue-green; the nightly water surface agitation expels any remaining excess.

Adjusting Without Killing Fish

Raise BPS in increments of half a bubble per second, then wait two to three days before the next adjustment. Watch the fish at the surface every morning. Gasping, glass surfing or hovering near the filter outlet means CO2 is too high or oxygen too low. Drop the rate and increase surface agitation. Most livestock losses to CO2 happen during quick adjustments, not at steady-state running.

Common Mistakes

Setting bubbles by sight without ever fitting a drop checker is the most common error. Tuning during the day when CO2 is at its plateau gives a misleading low reading; check at the same time each day for consistency. Forgetting to factor in hardscape volume on a heavily scaped tank means the actual water column is less than tank litres. A 90 litre tank packed with rock and substrate may hold only 65 litres of water.

Singapore Tap Water Notes

PUB water sits around 7.0 to 7.5 pH out of the tap with low KH. CO2 injection drops pH by roughly one full point at 30ppm dissolved gas, putting most planted tanks in Singapore at pH 6.5 during the photoperiod. This is fine for soft-water species but worth knowing if you keep livebearers or rift lake cichlids alongside plants.

Related Reading

Aquarium CO2 Measurement Guide Drop Checker pH
Best Aquarium Bubble Counter Guide
Best Aquarium CO2 Drop Checker Guide
Aquarium CO2 pH KH Relationship
How to Balance Light and CO2 Planted Tank