Opti­mize your Aquar­i­um’s CO2 Usage

All plants use CO2 in the process of pho­to­syn­the­sis — whether they’re under­wa­ter or not. With­out CO2 injec­tion, your tank’s plants are stuck rely­ing on the CO2 in your home­’s air dis­solv­ing into the water. So if you’re look­ing for bet­ter, health­i­er plant growth, CO2 injec­tion’s a requirement.

But— if you’re read­ing this arti­cle, you’re already using CO2!

Here’s the thing: you’re prob­a­bly not opti­miz­ing your CO2 in your aquarium.

You’re prob­a­bly wast­ing CO2 right now — I per­son­al­ly wast­ed so much when I was learn­ing about how to use it! Fear not, though: let’s dive into a few sim­ple changes you can make to start using CO2 more effectively.

1: Turn your Co2 on/​off at the right times.

Plants only use CO2 while they’re going through pho­to­syn­the­sis. When they’re not, plants actu­al­ly release CO2 into your aquar­i­um’s water.

As a result, hav­ing CO2 on ²⁴⁄₇ could poten­tial­ly cre­ate extreme­ly high con­cen­tra­tions in your tank. If you’re not tim­ing your CO2 release to align with your lights turn­ing on/​off, it could turn poten­tial­ly dead­ly, as CO2 over 30 ppm could be threat­en­ing to some tank fauna.

The opti­mal time to enable/​disable CO2 are two hours before lights-on, and one hour before lights-out.

Turn­ing CO2 on two hours before lights-on ensures that the water’s nice and sat­u­rat­ed when the plants being pho­to­syn­the­sis, and turn­ing CO2 off an hour before pre­vents any wast­ed CO2 from being dis­solved into the aquar­i­um’s water column.

We’d high­ly rec­om­mend plac­ing your CO2 and light­ing on a timer to pre­vent any pos­si­bil­i­ty of a sit­u­a­tion like this aris­ing in your tank, and wak­ing up to dead fish. You can find them all over the place online; here’s one that we’re par­tial to:

While timers are gen­er­al­ly quite reli­able, it’s always a good idea to do a man­u­al check every so often to ensure every­thing’s turn­ing on/​off as it should. We main­tain our equip­ment using AirTable, and have reminders set on a Google Cal­en­dar that tell us which piece of equip­ment needs check­ing, and when.

Increase your sur­face agitation

You’ve prob­a­bly read in the past that sur­face agi­ta­tion ​‘wastes’ CO2. While that’s tech­ni­cal­ly true — CO2 is dif­fused more read­i­ly at the air/​water bar­ri­er with agi­ta­tion—it’s only half the story.

Because you’re los­ing CO2 at that bar­ri­er, you’ll be replac­ing it as it’s lost. This ​‘cycle’ helps even­ly dis­trib­ute the CO2 through­out your tank, and can vis­i­bly improve the appear­ance and over­all health of your plant­ed tank.

As a bonus, sur­face agi­ta­tion also increas­es O2 lev­els, which helps pre­vent the ​‘biofilm’ at the sur­face of the tank. (That biofilm is an indi­ca­tor that your O2 lev­els aren’t as high as they should be, since the bac­te­ria are form­ing at the high­est con­cen­tra­tion of O2 — the surface.)

Use an inline diffuser

Some aquas­cap­ers love the micro bub­bles pro­duced from an in-tank dif­fuser, some hate it. Per­son­al­ly, I like the ​‘misty’ qual­i­ty that ceram­ic dif­fusers cre­ate, but I like plant-growth more. So I’ve used inline dif­fusers on most of my tanks.

Evi­dence shows that using an inline dif­fuser is the most effec­tive method of plac­ing CO2 into your aquar­i­um: they cre­ate micro bub­bles as well as dis­solved CO2, both of which have ben­e­fits to plants, and are marked­ly more effec­tive when used togeth­er. (Hav­ing those micro-bub­bles in phys­i­cal con­tact with the plants is ben­e­fi­cial, and inline dif­fusers dis­trib­ute these bub­bles more evenly.)

How do you opti­mize CO2?

Do you have any best-prac­tices for opti­miz­ing your CO2 usage? Per­haps you have a night­mare sto­ry to help dri­ve home the need for aquas­cape timers. Let us know in the com­ments below!