Category Archives: CO2

When to turn on your aquarium CO2…

CO2 is the single most important factor when growing plants in an aquarium (aside from light), and often the hardest to master. If you’ve never used CO2 before, one of the first things you might ask is when do I turn the CO2 on and off?

First of all, to be able to automatically turn your CO2 on and off requires a solenoid on your regulator. The solenoid allows you to determine exactly when your CO2 comes on and when your CO2 goes off. All you need to do is plug in your solenoid to a standard plug timer and set the timer when you want the on/off times. All our regulators come with a solenoid (I don’t see any reason why anyone would buy one without?). When to set the on/off timer is a common question we get!….

Setting the CO2 on/off times is easy, choosing when the best on/off times requires a bit more thought and experimentation! One’s thing for sure, the CO2 MUST come on before your lights do. This allows the CO2 levels inside your aquarium to build up to the required levels for your plants to grow. The accepted level of CO2 which is enough for plants to grow well and safe levels for fish is 30 parts per millions. The level of CO2 in your aquarium can be measured using a CO2 Drop Checker, a simple device which changes colour depending on the concentration of CO2 in your aquarium water. A green indication means you have the correct concentration of CO2.

So you’ve set your CO2 to come on before your lights come on, great! Next thing to do is to determine HOW LONG you need to turn it on before your lights in order to achieve the required levels of CO2 concentration for your plants (30 parts per million, GREEN indication on your drop checker). Depending on your tank set up, your CO2 ON time can vary quite a lot. The size of aquarium, type of diffuser, amount of surface agitation and your pattern of circulation can all effect the time you need to turn your CO2 on in order to achieve a green drop checker. The amount of time could vary from 1 hour up to 5 or more hours!

I would suggest doing a test whilst your lights are off and before you add fish. Try starting with 1 bubble per second and see if your drop checker has changed colour after an hour. If not, what about after 2 hours? 3 hours?  Try increasing your bubble count. Larger tanks will need more bubbles per second (measure using a bubble counter). Have you reached a green colour on your drop checker now? Excellent! If it has taken 3 hours for your drop checker to turn green by injecting 2 bubbles per second then set your CO2 timer to come on 3 hours before your light do.

Having the correct amount of CO2 when your lights come on is crucial for your plants. The beginning of your light period is the most important, you want your plants to start well. If not, they will be constantly trying to catch up with themselves for the remainder of the light period.

When you finally add fish, be sure to keep an eye on them during the first 1-2 days. CO2 toxicity kills, but only if we go above a certain level. A yellow drop checker could mean your fish suffering, keep an eye on this and adjust if necessary!

As for turning your CO2 off…try turning it off 30mins – 1 hours before your lights go off. Plants will use any remaining CO2 and after this the levels will start to drop. Plants do not use CO2 when they are not photosynthesising. So save yourself some CO2 and prevent gassing your fish by turning it off just before your lights.

You can find everything you need to get started with CO2 (minus the bottle) on our website by searching for CO2 Kits or by clicking here. Our CO2 kits contain a quality regulator, solenoid, diffuser, bubble counter and some CO2 tubing. Don’t forgot your drop checker kit too!

CO2 regulator & solenoid

Save money with a CO2 Solenoid Valve!

If you really want your plants to perform at their best then you will know by now that injecting CO2 into your planted aquarium is the way to go. But did you know your plants don’t always need this CO2 in the aquarium 24/7!?

That’s right, during light out your plants stop photosynthesising. Without light, there is nothing to trigger their growth. Therefore, CO2 (the other vital component needed for growth) is no longer required until the lights come back on again.

This means we can turn our CO2 off after the lights go out and back on again when the lights come on. Sounds like a boring task to do everyday doesn’t it!? Your bound to forget sometimes, and eventually you might end up just leaving it on all the time.

Well that’s unless you have a Solenoid valve to do the work for you. The Solenoid valve when attached to a electric timer will shut the CO2 on or off at the times you’ve pre set on your electric timer. Why waste good CO2 when the lights are out that is costing you money? More to the point, leaving your CO2 on over night can put your fish at risk. Whilst your plant aren’t using the CO2, levels of CO2 could build up in your aquarium so much that it could affect the health of your fish.


This piece of kit is so essential, we have attached one to all our regulators. We do not see the need to go without one.

If you would like to take a further look at our regulators with solenoid valve then click here.