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:
“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:
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?
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
(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)
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.
“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.
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
(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)
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