• Welcome to ScapeCrunch!

    We are a friendly, online community of people interested in planted aquariums. We support and help each other learn and grow. It is our sincere hope that you will join us and find our tight-knit community valuable and fun!

    ScapeCrunch is different than Facebook Groups. Here's how:

    • It is a place where you can make long-term friends in the planted aquarium hobby and have long, multi-day talks on specific subjects.
    • Unlike social media, online communities like ScapeCrunch are much better at curating collective knowledge and in fostering deeper relationships.
    • They lend themselves better at long-form discussions.
    • You can maintain a thread on your personal aquarium with pictures and details. Other members can comment, help and ask questions. You can do the same with their Member Tank threads.

    Where Facebook is more like a large city-wide party, ScapeCrunch is more like your neighborhood bar "where everybody knows your name. And they're always glad you came." It's always fun to go to large parties but it's at the local bar that you feel people really know you. The great part is that you can and should go to both!

    Please consider joining to become a full fledged member of our growing community of planted aquarium obsessed enthusiasts. Let's grow together!

    Join Us!

Sera active CO2 reactor – a meaningful innovation?

Yugang

Active Member
Supporting
Joined
May 8, 2023
Messages
362
Reaction score
841
Location
Hong Kong
A couple of years ago I had enough of diffusers in my tank and researched options for CO2 reactors. The most popular, used for decades already, were the Cerges and Rex Griggs style where bubbles are injected into a vertical water column with a waterflow that keeps the CO2 bubbles long enough moving around to get fully dissolved. Aiming to optimize these reactors many variations were tried including bio balls, venturis, needle wheels, sponges, diffusers, and vortexes.

The optimization of a CO2 reactor is to have:
  • Sufficient CO2 absorption capacity for a given size of the tank and a given target CO2 ppm.
  • Ease to set up, leak-free, robust build.
  • No noise.
  • No CO2 bubbles escaping into the tank, 100% efficiency.
  • Minimal flow reduction of water pump, or cannister filter.
  • Minimal or no maintenance, wear or moving parts.
  • Low cost of purchase and maintenance.
Sera promotes their reactor as
The new sera flore CO2 active reactors 500 and 1000 with twin rotor supersede the generation of static CO2 reactors. The rotors, the upper one of which is designed as a lamella rotor (6.3), ensure strong blending of CO2 with the aquarium water, allowing to dissolve several hundred CO2 bubbles per minute.”
The sera active reactors are designed for optimized currents, provide excellent performance capacity, and can completely dissolve even large amounts of CO2. They can entirely be disassembled and are therefore easy to maintain and clean.

So how does the Sera concept differ from the Rex Griggs and Cerges concept:
  • While in the Rex Griggs CO2 bubbles are injected into the water column (typically half-way), the Sera reactor (quote from the manual) “The water current (4.1) of the pump drives the double rotor (4.2) integrated in the reactor, which disperses CO2 introduced from the pressure gas bottle (4.3) so finely that it entirely dissolves in water. Even large amounts of CO2 can be dissolved entirely if required, allowing to supply even large, densely planted aquariums with CO2 economically” (end quote).
  • As the Sera double rotor is in the vertical water column, it will drive a rotation in the reactors water column.

1712883912595.png




A couple of years ago, after a careful review I decided not to buy this reactor. As I do not own it, I refer to the user manual and this Youtube video.


So how much CO2 does this reactor inject, and for what tank size is it suitable?
  • The ‘reviewer’ in the Youtube video uses the reactor on a 70 l tank, and we can see that there is only CO2 in the top of his reactor while no CO2 bubbles in the water column. This reminds me of ‘test driving’ a car while being parked in the dealer’s showroom, and extrapolating that experience to what it must be like on the highway.
  • The Sera manual says “The sera flore CO2 active reactor 500 is suitable for freshwater aquariums between 250 l (66 US gal.) and 600 l (159 US gal.). We recommend the sera flore CO2 active reactor 1000 for larger or densely planted aquariums” (end quote) but it does not specify any CO2 ppm targets. Reading further we find some vague reference “The performance capacity of the reactor is sufficient to create a pH value of 5.9 if the unit is operated without limiting” (end quote), but no reference is made to degassed pH value or pH drop and the statement is therefore meaningless.

So how about ease of installation? For some reason, even on this rather complex build, Sera did not include a degas valve. We see in the video, time stamp 5:40, that a big air pocket remains after initial filling with water, and per instruction in the manual “You must briefly turn the unit around or hold it upside down as to remove air. This will allow air to escape through the outlet tube near the bottom of the reactor. Repeat this process until there is no air left in- side the reactor if necessary. Then the sera active reactor 500 or 1000 is brought back into an upright operation position and fastened” (end quote) the reviewer holds the reactor upside down in his cabinet and is fortunate that his tubes are long and flexible enough for doing that. The problem is that this is not a one-time hassle, as any vertical reactor will gradually build up some gas and needs to be degassed (the pump may blow in some air, but also basic physics processes desorbing gases from the water having the same effect). A simple degas valve could have addressed all this, easy for initial setup and perhaps a weekly quick degas of the reactor.

How about noise? We see in the video, timestamp 8:30 that a gas pocket forms in the top of the reactor, where water splashes on the rotor. Go to timestamp 9:35, or review several other Youtube videos to learn that the reactor does not make excessive noise, but is not silent either. The point is however, that reactors that have no rotors and simply inject CO2 in the water column can be made perfectly silent.

How about the rotation of the water column? True, when observing CO2 bubbles spiraling down through the reactor it looks like the dwell time of each bubble seems to be longer than in a water column that is not rotating. But our intuition here is misleading. The vertical component of the bubbles motion is unaffected by the horizontal components, and indeed the rotation (movement in horizontal plane) does not increase the dwell time. The correct way, perhaps counterintuitively, to see it is that the dwell time is almost entirely dependent on the vertical component of the motion of the water column and the rotation is just an optical illusion in this regard.

So how about loss of flow from the pump/cannister? All reactors with bubbles in a vertical flow will create a back pressure and reduction of flow from the pump. This can be easily understood from the principle of an air lift pump, but unfortunately the pumping action from the bubbles works against our pump powering the cannister and reactor. The Sera reactor makes matters worse, as the energy from our pump is now also dissipated by the action of the rotors and the rotating water column. How much losses are caused by the rotor and water column rotation is difficult to say, but the point is that it is unnecessary to start with as the rotation does not add value compared to a much simpler Rex Grigg reactor.

How about maintenance? The Sera reactor is more complex than a simple functional Rex Grigg reactor, with more parts and unlike other reactors it has moving parts. The manual says “The rotors (6.3 and 6.4) may wear out after having been in operation for a longer time, also the O-ring seal (6.2) should be replaced after having the unit disassembled several times. These parts are available as spare parts” (end quote).

Our hobby is not entirely rational, and the marketing that Sera does claiming “The new sera flore CO2 active reactors 500 and 1000 with twin rotor supersede the generation of static CO2 reactors” may work for them. Whether it is a meaningful innovation from a functional perspective, or pricing perspective is a different question and all of the above is of course just my personal analysis and opinion and I do respect different perspectives.

Finally, a hint to the Sera R&D team :unsure: (Reactor dimension can be calculated from tanks dimensions and CO2 ppm target, no noise, no bubbles, no flow reduction, no moving parts, compact and affordable)

1712884398168.png
 
Last edited:
eehhh.. this thing has been around for more than a 'couple years.' :) Amazon shows it as being available since
  • Date First Available ‏ : ‎ February 16, 2012
That sounds about right... it came out not too long after I used an ista version of it.

81P-G1c0n0L._AC_SL1500_.jpg


Everything you've mentioned hit the nail on the head. I daresay the intention was in the school of chop up the bubbles and swish them around to encourage them to dissolve better.

During my use, inevitably, the spinners up top would get stuck. Bad quality rotors, wear, algae, detritus, co2 exceeding dissolution rate, you name it.

Then a gas pocket will form and any efficiency gained from the rotors will be gone. No degas means its a nightmare to get that bubble out. and mine was internal, so it was even more of a bother!
 
the intention was in the school of chop up the bubbles and swish them around to encourage them to dissolve better.

I used a modified (indeed the standard product was not perfect) Aquamedic reactor for years, and with modifications I got it to work nearly perfectly. No noise, 100% CO2 absorption, no mist or bubbles in the tank and stable CO2 ppm. My dissatisfaction was that for decades we as hobbyists have been trying many many variations on Cerges and Rex Griggs, trial and error, and that still nobody had developed a stable solution that would always work - for each tank size, for each CO2 ppm target, for each water pump flow. This is of course not really encouraging for new hobbyists who want to inject CO2, and from them we got endless posts on fora asking for help.

What I did not mention in the previous post is that the Sera does not have a bypass, so it will be impossible to optimise the flow when using too strong pumps that may blow bubbles into the tank (Sera only mentions minimum pump capacity, not maximum). When we watch timestamp 9:00 in the Youtube video above, we see that the poster also plays with the idea to add a sponge to his Sera reactor, as this "next generation" commercial product does not fully satisfy him even when only testing it far below its rated capacity.

So the trial and error goes on, same confusion but just at a higher level.

From a physics perspective making small bubbles of gas in a fluid can be easy, and it can be hard. It can be easy when the gas comes at high pressure or energy, like from a cylinder, and we use a diffuser with small pores. It can be hard when gas comes at low pressure, we can't use a diffuser, and in that case we would need a needle wheel, or a rotor for chopping up the large bubbles into small bubbles. From a technology perspective, please note Sera and Ista, it makes absolutely no sense to first give away the advantage of having high pressure gas available, then no longer having the obvious solution of using a diffuser, and then start using needle wheels or next generation lamella rotors to do the chopping the hard way and at the cost of noise, flow reduction, bubbles, maintenance and spare parts.

If you want small bubbles (in fact you shouldn't), just use an air stone and keep it simple.

Very few hobbyists will have the motivation to really dig into these technical issues, just because it is a hobby and is meant to make our arms wet and relax when doing what we like most. My message here is to the manufacturers, as professional partners to the hobby and applying serious science and technology on the products they are selling.
 
Last edited:
Good stuff Yugang

Some personal exp

Im running this 1000 model currently on a 50 gal, for prob a couple years now. The inline you see wasnt cutting it, had flow to spare so I just spliced in the little reactor, which I had from a long time ago

20240412_210255.jpg

At peak for most of the day there's a 3-4" gas pocket on top. I could probably fine tune it down a little bit but Im too lazy. Being gas it goes away in an hour or two after co2 cuts off. This reactor would run the 50 by itself with about the same result. I did run a 75 gal with it 10-12 years ago when I was new to the co2 game. Did the job, barely, cuts the flow way down

Here's the smaller 500. For anyone using or buying it, be very careful with the little stem that the co2 line attaches to. They break off very easy. The 1000 above is broke off, hole sealed with...something I dont remember exactly what I used

20240412_210346.jpg

You can take the little spinning wheel out and it works just the same, will probably be a little quieter. As mentioned it doesnt help anything to begin with

Final thoughts the larger 1000 would suffice for 40-50 gal tanks. I wouldnt try it on on anything bigger. Lolol at Sera's tank size claims. The 500 is OK from say 20-40 gal

But these days it would not be my first choice for a reactor...or even my second. Especially after reading @Yugang 's evisceration of the design here
 
Last edited:
You can take the little spinning wheel out and it works just the same, will probably be a little quieter.
That sounds like a good idea, and then turn it by 90 degrees and see what that does.....

1712985378426.png

Be careful not to gas your fish, because while it looks underwhelming without its double lamella rotor and bubbles in a vortex, it is probably much more powerful now. If you send me the dimensions, length and diameter at half-length, I can run some calculations.

Horizontal CO2 Reactor - Yugang 鱼缸 Reactor
 
Very interesting

Here ya go, this is inches

20240413_011504.jpg

20240413_011531.jpg


The 1000 model is exactly the same, just longer. Top parts all interchange

20240413_011621.jpg

All the inner pieces can be removed to just have the empty chamber. I was gonna say for horizontal you could take out the inner tube, but on second thought youd need that to put the return pathway on the opposite end, right?
 
Very interesting

Here ya go, this is inches

View attachment 4781

View attachment 4782


The 1000 model is exactly the same, just longer. Top parts all interchange

View attachment 4783

All the inner pieces can be removed to just have the empty chamber. I was gonna say for horizontal you could take out the inner tube, but on second thought youd need that to put the return pathway on the opposite end, right?
They are actually quite small, if the smallest is recommended for tanks up to 600 liter then Sera is quite smart to keep us guessing about the CO2 ppm.

If we assume the cross section of the smallest to be about 8.5 * 2 inch2, 11.000 mm2, then applying the 17.7 ratio we expect this reactor in horizontal mode to push 1.5 pH drop on a tank with a 19.400 mm2 surface area. This would correspond to a 60-P tank.

The large reactor would be 11 *2 inch2, 14.000 mm2, and would push 1.5 pH drop on a 25.000 mm2 tank. If we accept a 1.2 pH drop target, this would be a factor of 2 in CO2 ppm we could achieve this with a tank with 50.000 mm2 surface area. A 120-P tank comes closest with 540.000 mm2.

We would keep the inner tube, and if I interpret the photos well there is a good chance that even overflow mode will work.
 
A couple of years ago I had enough of diffusers in my tank and researched options for CO2 reactors. The most popular, used for decades already, were the Cerges and Rex Griggs style where bubbles are injected into a vertical water column with a waterflow that keeps the CO2 bubbles long enough moving around to get fully dissolved. Aiming to optimize these reactors many variations were tried including bio balls, venturis, needle wheels, sponges, diffusers, and vortexes.

The optimization of a CO2 reactor is to have:
  • Sufficient CO2 absorption capacity for a given size of the tank and a given target CO2 ppm.
  • Ease to set up, leak-free, robust build.
  • No noise.
  • No CO2 bubbles escaping into the tank, 100% efficiency.
  • Minimal flow reduction of water pump, or cannister filter.
  • Minimal or no maintenance, wear or moving parts.
  • Low cost of purchase and maintenance.
Sera promotes their reactor as
The new sera flore CO2 active reactors 500 and 1000 with twin rotor supersede the generation of static CO2 reactors. The rotors, the upper one of which is designed as a lamella rotor (6.3), ensure strong blending of CO2 with the aquarium water, allowing to dissolve several hundred CO2 bubbles per minute.”
The sera active reactors are designed for optimized currents, provide excellent performance capacity, and can completely dissolve even large amounts of CO2. They can entirely be disassembled and are therefore easy to maintain and clean.

So how does the Sera concept differ from the Rex Griggs and Cerges concept:
  • While in the Rex Griggs CO2 bubbles are injected into the water column (typically half-way), the Sera reactor (quote from the manual) “The water current (4.1) of the pump drives the double rotor (4.2) integrated in the reactor, which disperses CO2 introduced from the pressure gas bottle (4.3) so finely that it entirely dissolves in water. Even large amounts of CO2 can be dissolved entirely if required, allowing to supply even large, densely planted aquariums with CO2 economically” (end quote).
  • As the Sera double rotor is in the vertical water column, it will drive a rotation in the reactors water column.

View attachment 4766




A couple of years ago, after a careful review I decided not to buy this reactor. As I do not own it, I refer to the user manual and this Youtube video.


So how much CO2 does this reactor inject, and for what tank size is it suitable?
  • The ‘reviewer’ in the Youtube video uses the reactor on a 70 l tank, and we can see that there is only CO2 in the top of his reactor while no CO2 bubbles in the water column. This reminds me of ‘test driving’ a car while being parked in the dealer’s showroom, and extrapolating that experience to what it must be like on the highway.
  • The Sera manual says “The sera flore CO2 active reactor 500 is suitable for freshwater aquariums between 250 l (66 US gal.) and 600 l (159 US gal.). We recommend the sera flore CO2 active reactor 1000 for larger or densely planted aquariums” (end quote) but it does not specify any CO2 ppm targets. Reading further we find some vague reference “The performance capacity of the reactor is sufficient to create a pH value of 5.9 if the unit is operated without limiting” (end quote), but no reference is made to degassed pH value or pH drop and the statement is therefore meaningless.

So how about ease of installation? For some reason, even on this rather complex build, Sera did not include a degas valve. We see in the video, time stamp 5:40, that a big air pocket remains after initial filling with water, and per instruction in the manual “You must briefly turn the unit around or hold it upside down as to remove air. This will allow air to escape through the outlet tube near the bottom of the reactor. Repeat this process until there is no air left in- side the reactor if necessary. Then the sera active reactor 500 or 1000 is brought back into an upright operation position and fastened” (end quote) the reviewer holds the reactor upside down in his cabinet and is fortunate that his tubes are long and flexible enough for doing that. The problem is that this is not a one-time hassle, as any vertical reactor will gradually build up some gas and needs to be degassed (the pump may blow in some air, but also basic physics processes desorbing gases from the water having the same effect). A simple degas valve could have addressed all this, easy for initial setup and perhaps a weekly quick degas of the reactor.

How about noise? We see in the video, timestamp 8:30 that a gas pocket forms in the top of the reactor, where water splashes on the rotor. Go to timestamp 9:35, or review several other Youtube videos to learn that the reactor does not make excessive noise, but is not silent either. The point is however, that reactors that have no rotors and simply inject CO2 in the water column can be made perfectly silent.

How about the rotation of the water column? True, when observing CO2 bubbles spiraling down through the reactor it looks like the dwell time of each bubble seems to be longer than in a water column that is not rotating. But our intuition here is misleading. The vertical component of the bubbles motion is unaffected by the horizontal components, and indeed the rotation (movement in horizontal plane) does not increase the dwell time. The correct way, perhaps counterintuitively, to see it is that the dwell time is almost entirely dependent on the vertical component of the motion of the water column and the rotation is just an optical illusion in this regard.

So how about loss of flow from the pump/cannister? All reactors with bubbles in a vertical flow will create a back pressure and reduction of flow from the pump. This can be easily understood from the principle of an air lift pump, but unfortunately the pumping action from the bubbles works against our pump powering the cannister and reactor. The Sera reactor makes matters worse, as the energy from our pump is now also dissipated by the action of the rotors and the rotating water column. How much losses are caused by the rotor and water column rotation is difficult to say, but the point is that it is unnecessary to start with as the rotation does not add value compared to a much simpler Rex Grigg reactor.

How about maintenance? The Sera reactor is more complex than a simple functional Rex Grigg reactor, with more parts and unlike other reactors it has moving parts. The manual says “The rotors (6.3 and 6.4) may wear out after having been in operation for a longer time, also the O-ring seal (6.2) should be replaced after having the unit disassembled several times. These parts are available as spare parts” (end quote).

Our hobby is not entirely rational, and the marketing that Sera does claiming “The new sera flore CO2 active reactors 500 and 1000 with twin rotor supersede the generation of static CO2 reactors” may work for them. Whether it is a meaningful innovation from a functional perspective, or pricing perspective is a different question and all of the above is of course just my personal analysis and opinion and I do respect different perspectives.

Finally, a hint to the Sera R&D team :unsure: (Reactor dimension can be calculated from tanks dimensions and CO2 ppm target, no noise, no bubbles, no flow reduction, no moving parts, compact and affordable)

View attachment 4767
I ran one of those back in 2018/2019. As soon as any detritus accumulates, the rotor stops spinning anyways, lol. I haven't bothered with it in years
 
I’m about to pick up one of these to try out for the hell of it. I was planning on running it while I removed the inline diffuser for cleaning and see how it compares. Now I’m considering mounting it horizontal and logging some data.
 
I used this for a 75g back in 2018. It worked well at a lower co2 injection rate. I tried it recently for my 125 and it just makes too much noise for the rate of co2 required. This is why I switched to YG's horizontal reactor and I'm never looking back.
 
Back
Top