Anybody use passive Co2?

[Corbidorbidoodle]

I was at the CoOp a couple days ago and I saw they're using a passive CO2 bell in their big display tank. I didn't even know that was a thing!

I'm really in to heavily planted, low-tech tanks. I don't really want the expense of a CO2 injection system. And I definitely don't want the maintenance. It seems cool that the plants are brighter and fill in quickly, but I only have to trim about once a month. I've also read that fluctuating CO2 is real bad (good?) for algae. And I know I'd be terrible about getting the canister refilled.

Are any of you using a passive system? How do you like it? What size are your tanks? I'd start with my 55. That's the one I battle a little algae in regularly.

Do you guys fill up in the morning or the evening? Can I stop using CO2 and not have my plants die? Do you still use an airstone for oxygenation?

Sorry for so many questions. There are a lot of answers on the WWW, but people here are so helpful and provide personal experience rather than just something they read once.

[Tihshho]

Passive systems used to be all over the place over 10 years ago. I think Fluval had one as well as a few other companies that had yeast based reactors feeding into a passive bell. IME those systems were junk as they needed to be precise in order to get clean CO2 put into the captive container. I've seen others, even some other stores besides ACO, use passive systems by having a large tank with a long hose that terminated to an air gun style sprayer and they would fill up inverted glass bottles daily for the tanks to have a CO2 source with pretty good success. 

Getting clean presurized CO2 is key, so if you're going to invest in that, you might as well get a regulator so you don't forget to fill up the 'bell' or whatever container it is that you're capturing the CO2 in. If you're worried about your CO2 running out, just get two bottles. Once one runs out swap to the other and you'll have time to get the first empty traded out for a filled one. I used to run 2.5lb tanks for the longest time, and I ended up swapping to 5lb tanks which lasted a ton longer. One day when I went to swap out the 5lb tank at my local welding gas shop, they didn't have any 5lb'ers in stock so the guy upgraded me to a 10lb tank for no extra cost. I had been using 10lb's since and they last for what seems to be forever.

[Seattle_Aquarist]

On 5/4/2022 at 9:37 AM, Corbidorbidoodle said:

I was at the CoOp a couple days ago and I saw they're using a passive CO2 bell in their big display tank. I didn't even know that was a thing!

I'm really in to heavily planted, low-tech tanks. I don't really want the expense of a CO2 injection system. And I definitely don't want the maintenance. It seems cool that the plants are brighter and fill in quickly, but I only have to trim about once a month. I've also read that fluctuating CO2 is real bad (good?) for algae. And I know I'd be terrible about getting the canister refilled.

Are any of you using a passive system? How do you like it? What size are your tanks? I'd start with my 55. That's the one I battle a little algae in regularly.

Do you guys fill up in the morning or the evening? Can I stop using CO2 and not have my plants die? Do you still use an airstone for oxygenation?

Sorry for so many questions. There are a lot of answers on the WWW, but people here are so helpful and provide personal experience rather than just something they read once.

Hi @Corbidorbidoodle

Before I went out and bought a CO2 system I did DIY yeast CO2 fed into the input of my Aquaclear HOB filter - I wanted to verify if I would see better plant growth or not.  I was impressed with the improvement in growth and plant health but did not like having to do the bottle change out every 3-4 days.  After six months or so I bought a CO2 system and have never looked back. 

You stated that you 'don't want the maintenance' of a CO2 system.  I can assure you a CO2 system is a lot less maintenance than a passive CO2 system if your CO2 cylinder is large enough.  For example I have a 20# cylinder providing CO2 to three tanks (45, 30, 20H) and I have to get it refilled about every 16 months.  Don't have to touch any needle valves and I don't use bubble counters so no maintenance. The 5# cylinder runs my 75 gallon about 2-3 months before I need to refill it.  -Roy

[Corbidorbidoodle]

Yeah, that all sounds good.

Maintenance wise, I was thinking  more of trimming the plants. People talking about having to trim CO2-ed plants every week or more. I just like doing it every month or so. I was thinking the passive CO2 would be just enough they they grow better, but not super fast. Like, just a nudge.

And I imagine I'd go through less CO2 as well, right? Or does it use about the same as a typical diffuser? Is that the right word? Typical injection? You get what I'm saying.

And I figured regarding fluctuating CO2 levels, this passive type system would be a little more forgiving since there's not that much going in.

[Tihshho]

Passive systems need a large area to capture adequate amounts of useable CO2 as well as need to have a lot of surface area and flow under the bubble of CO2 for it to be 'absorbed' into the water column. Larger the tank, larger the container. 

Depending on the plants you choose you will have to trim more than others. Stem plants grow like weeds, anubias and crypts get bushy. If you inject CO2 with the right plants you won't have to trim much. 

[Ogpulchra]

I inject co2 at about 2-3 bubbles a second in my 40 gallon breeder and it made a huge difference in plant health and algae control. The stem plants do grow a little faster, but I only have to trim once a month. 

 

[Ben Ellison]

I looked into passive and diy CO2 and ultimately went with 5lb cannister and regulator and I absolutely love it. Well worth the 150 bucks it cost to get setup.

[Tihshho]

If you go the pressurized CO2 route, do yourself a favor and save the money of not trying out the off the shelf DIY systems or the paintball/sodastream setups. The regulators and solenoids for the standard tanks perform a ton better and more reliably. The off the shelf DIY systems take a lot of daily monitoring until you get a balance in your CO2 generating mixtures. Not only that, they are not reliable for those who ever are away from home (think about what happens if you're on vacation.) The paintball/sodastream setups look cheaper upfront, but then the regulators for paintball systems seem to fail or not produce a reliable dosage of CO2, then the sodastream cans you have to invest in replacement tanks when you need to 'refill'. Cheap upfront isn't cheap down the line. 

The used market is flooded with regulators. I can't tell you how many I've seen or snagged myself over the years. Intended purchases and not. I picked up a used rimless ADA tank from someone and when I went to pick it up they threw in 2 regulators just cause they wanted them gone as they no longer had the tanks. One brand to be weary of for regulators, and this might have changed, is Milwaukee. They used to have a known problem that at the end of the tank pressure would purge the remaining contents of the tank regardless of your valve settings. I'm not sure if this is still a problem, but they used to be the cheapest off the shelf setups available. Can't count the amounts of issues I've read on various forums, customers I dealt with, and totals of tens of thousands of dollars of fauna lost due to that bad design.