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:
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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!