Ideas why Rex Grigg reactor isn't dissolving CO2 efficiently?

13251 Views 41 Replies 10 Participants Last post by Remmy, Apr 30, 2017

Supa Mint

Discussion Starter · Feb 1, 2017 (Edited)

Background:
I was previously using an Atomic in-line diffuser to supply pressurized CO2 to my 29 gallon aquarium. My dual-compartment CO2 drop checker, with fresh 4 dKH indicator solution, indicated ~30ppm at about 2 bps (bubbles per second).

But my tank was filled with unsightly micro-CO2 bubbles; and I felt that my drop checker may be giving a false reading, by measuring the CO2 bubbles, rather than the CO2 that was fully dissolved in the water.

So I ordered a beautifully built and finished Rex Grigg reactor from NilocG. The micro-CO2 bubbles are gone, which is a great aesthetic improvement; however, I can’t get my drop checker to quite reach 30ppm of CO2, even at >10 bps!

So what is wrong? Where is the CO2 going? If there are no visible CO2 bubbles, then why is CO2 not dissolved in the water?

Troubleshooting: I have tested for CO2 leaks by spraying soapy water on the CO2 junctions, unions, and fittings, but don’t see anything.

Observation/Theory: The reactor is silent when the CO2 is off. However, I can hear water/gas interacting in the reactor within about an hour of the solenoid starting the CO2 flow. The water/gas mixing sound gets louder throughout the 6 hour photoperiod , making me think that there may be a CO2 gas layer forming in the reactor. Is it possible that the water flow (top-to-bottom) is ‘falling through’ the CO2 gas later, rather than mixing and dissolving? If so, would some back pressure, via an adjustable valve on the output side of the reactor help the CO2 dissolve in the water? I'm running at 275 gph via an Eheim 2073 cannister filter.

Thank you in advance for any advice or suggestions!

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burr740

· #2 · Feb 1, 2017

Supa Mint said:
would some back pressure, via an adjustable valve on the output side of the reactor help the CO2 dissolve in the water?

Not sure it will solve the entire problem but yes, this will help a lot.

Craigthor

· #3 · Feb 1, 2017

Possible reactor is too short for the flow so you get the buildup at the top.

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Immortal1

· #4 · Feb 1, 2017

Another possible issue might be your mounting location of the reactor. Ideally you would want the output of the reactor (the bottom) to be as low as possible - preferably just as low as the bottom of the canister filter. What this does is use the water column head pressure to it's fullest extent to increase the pressure inside the reactor to squeeze the co2 bubbles (but does not slow down canister flow). Putting a valve on the output of the reactor also adds pressure to the inside of the reactor (same effect) but does slow down your flow.

PlantedRich

· #5 · Feb 1, 2017

Is there still room for expressing different views in the current toxic environment?

Some thoughts on different ideas to start. Water pressure increases about .4 to .5 PSI for foot of height. So moving the reactor even six feet will change the pressure less than 3 PSI. That's not going to make much difference is it?
If the CO2 is leaving the reactor, it is going into the water so you are likely to be getting more in. Mag drive filter pumps generate almost no measurable PSI. I might guess less than 1PSI, so using a restriction will only cut the flow. Even algae in the tubing is enough to cut filter flow.

Some things that I see may happen without you thinking about them. One is that the point where the CO2 enters probably changed and it is probably not getting to the drop check in the same way.
Things I would check are how the water circulates and where the two items are located. If the drop check was reading near the former point like maybe above it and it is now across the tank and the CO2 is coming in at the top like through a spraybar, the reading will be different. You may find running the return filter flow down to near the bottom will get more CO to stay in the water.
I no longer use spraybars with CO2 as it blows too much back into the air. I use powerheads to maintain surface movement.

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Supa Mint

Discussion Starter · #6 · Feb 1, 2017

burr740 said:
Not sure it will solve the entire problem but yes, this will help a lot.

Thanks - adding some backpressure will probably be my next attempt to improve the dissolving of CO2.

Craigthor said:
Possible reactor is too short for the flow so you get the buildup at the top.

The reactor is 20" long. The CO2 buildup eventually resolves itself after the solenoid (and light) shuts off for the night - which means that I'm probably dosing (undissolved) CO2 for longer than necessary.
Do you think that the gas layer buildup makes CO2 dissolving less efficient? Gas (CO2) is much more compressible than liquid (H2O), so a CO2 layer wouldn't have the 'force' to dissolve.
Do you think that reducing the water flow rate (it's adjustable) would improve the CO2 dissolving? Or would this just allow for an even larger gas layer? Plus, I would hate to reduce filtration (flow) unless necessary.

Immortal1 said:
Another possible issue might be your mounting location of the reactor. Ideally you would want the output of the reactor (the bottom) to be as low as possible - preferably just as low as the bottom of the canister filter. What this does is use the water column head pressure to it's fullest extent to increase the pressure inside the reactor to squeeze the co2 bubbles (but does not slow down canister flow). Putting a valve on the output of the reactor also adds pressure to the inside of the reactor (same effect) but does slow down your flow.

Thanks, I see your point. However, the reactor output (and the cannister filter) is on the floor. So, unfortunately, I can't add additional pressure by lowering any further.

PlantedRich said:
.... Some things that I see may happen without you thinking about them. One is that the point where the CO2 enters probably changed and it is probably not getting to the drop check in the same way.
Things I would check are how the water circulates and where the two items are located. If the drop check was reading near the former point like maybe above it and it is now across the tank and the CO2 is coming in at the top like through a spraybar, the reading will be different. You may find running the return filter flow down to near the bottom will get more CO to stay in the water.
I no longer use spraybars with CO2 as it blows too much back into the air. I use powerheads to maintain surface movement.

Ok, these are interesting points - thank you.
1. Location of drop checker and spray bar are the same as previous (although the flow/circulation rate could be slightly different now).
2. Generally, I feel that circulation is 'decent' and CO2 loss at surface is minimal: 275gph in 29 gallon tank; spray bar mounted vertically; almost no surface agitation (bad for fish); plants all swaying (I've struggled to keep plants from blowing over by deflecting/angling spray bar into back glass).
3. Filter return flow at bottom (corner)

This all leads me to believe that my previous CO2 readings with the inline filter (and with lots of micro-CO2 bubbles) were falsely elevated by bubbles getting under the drop checker. But I still can't figure out why I can't get the drop checker to crack 30ppm with such a high bps rate.

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PlantedRich

· #7 · Feb 1, 2017

The devil is often in the details? It may take a bit to get figured what is happening.

Meanwhile there is another current post that somewhat shows what I find on the pressure in reactors.
http://www.plantedtank.net/forums/9-equipment/1119826-need-reactor-advice.html

With the very short water column and a very tiny, weak mag drive motor, we not have enough pressure to measure as is shown in that post. there is some pressure there but likely just not enough to measure and show on a meter reading 0-100. I have no idea how much increase in pressure we might need but then I find it hard to figure how to get that pressure increase when talking about a plastic pipe with plastic tubing which is almost a basic open at both ends.
Seems to me that we would need to cork up both ends of the tubing to get any real pressure in the reactor.

When I think of building pressure in a reactor, I think of trying to blow up an air mattress with a hole in it!

burr740

· #8 · Feb 1, 2017

Anyone who doesnt believe restricting the outflow, even a little bit, can increase the pressure enough to make a HUGE difference in the final dissolution of tiny micro bubbles..... has never tried it for themselves.

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milesm

· #9 · Feb 1, 2017 (Edited)

you said that the flow rate/circulation pattern could be different than what it was before. many report reduced flow rates when going through a reactor. these changes could account for your current lower co2 levels, especially if spraybar and drop checker are in the same location.

i think your drop checker overestimated co2. as you said, the mist from the atomic was driving it green which means that you had less than 30ppm co2. at 2bps on a 29g, i'm almost certain it was indeed, less than 30.

you could also try turning co2 on an hour or two before lights on, and turn it off an hour or so before lights off.

how was plant growth using the atomic? what do plants look like with the reactor so far?

Supa Mint

Discussion Starter · #10 · Feb 2, 2017

PlantedRich said:
....When I think of building pressure in a reactor, I think of trying to blow up an air mattress with a hole in it!

burr740 said:
Anyone who doesnt believe restricting the outflow, even a little bit, can increase the pressure enough to make a HUGE difference in the final dissolution of tiny micro bubbles..... has never tried it for themselves.

Ok, I have just started an experiment to test an increase in back pressure. I have used a vise-clamp to pinch/flatten the tubing after the reactor. This is a very unscientific study, since I have no way to know the volume reduction or pressure increase (if any). But if the drop checker indicates an increase in CO2, then I can conclude that my cannister filter can handle some back pressure; and that dissolved CO2 is increased with back pressure.

milesm said:
....you could also try turning co2 on an hour or two before lights on, and turn it off an hour or so before lights off.

how was plant growth using the atomic? what do plants look like with the reactor so far?

Thanks, I currently turn the CO2 on 1 hour before lights; and off 30 minutes before dark. I just can't quite get the drop checker to hit desired 30ppm of CO2, regardless of how long CO2 is on, or at any bps.

I hesitate to compare the plant growth with the inline diffuser to the reactor, since I changed fertilizer strategy to EI at the same time. But plant growth appears to be better; and algae growth has possibly decreased. I just can't seem to get the CO2 level increased to the level that I desire (>30ppm).

PlantedRich

· #11 · Feb 2, 2017

I feel a restriction on the outflow will change the amount of bubbles seen coming out. However, I do not agree that this is caused by an increase in pressure but I feel it is far more likely to be the reduced flow making the contact time much more. I fully agree that I have not used any form of flow restriction but when I did get some bubbles escaping, I did not want to reduce flow as I want my filters to perform as well as possible.
I found that creating a longer dwell time inside the reactor by increasing either the length or diameter of the PVC worked to remove the bubbles without cutting the flow.
My basic thought is that we do know that CO2 will move into the water when given time. That is the whole idea of both the Cerge's and the Grigg's. I also see the other post which shows there is no measurable pressure inside the reactor as the poster has it. So does anybody have a meter or other info showing us how this pressure is developed when the system is open to the tank water at both ends? I see no reason for much increased pressure but I do see there will be less flow. Less flow gives longer time for the CO2 to move into the water. This is one of the variables that I try to estimate when I build a reactor for a different size tank or filter. I find I have to size the reactor to fit both the flow from the filter and the amount of CO2 I expect to push into the tank. When I get it wrong, I cut the PVC and add a couple more inches to the length but I do not ever want to restrict the flow.
I'm willing to change my mind if there is somebody with a meter on their system and they can show a pressure increase by reducing flow.

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burr740

· #12 · Feb 2, 2017

PlantedRich said:
I feel a restriction on the outflow will change the amount of bubbles seen coming out. However, I do not agree that this is caused by an increase in pressure but I feel it is far more likely to be the reduced flow making the contact time much more. I fully agree that I have not used any form of flow restriction but when I did get some bubbles escaping, I did not want to reduce flow as I want my filters to perform as well as possible.
I found that creating a longer dwell time inside the reactor by increasing either the length or diameter of the PVC worked to remove the bubbles without cutting the flow.
My basic thought is that we do know that CO2 will move into the water when given time. That is the whole idea of both the Cerge's and the Grigg's. I also see the other post which shows there is no measurable pressure inside the reactor as the poster has it. So does anybody have a meter or other info showing us how this pressure is developed when the system is open to the tank water at both ends? I see no reason for much increased pressure but I do see there will be less flow. Less flow gives longer time for the CO2 to move into the water. This is one of the variables that I try to estimate when I build a reactor for a different size tank or filter. I find I have to size the reactor to fit both the flow from the filter and the amount of CO2 I expect to push into the tank. When I get it wrong, I cut the PVC and add a couple more inches to the length but I do not ever want to restrict the flow.
I'm willing to change my mind if there is somebody with a meter on their system and they can show a pressure increase by reducing flow.

If it was solely due to increased dwell time then cutting the flow before the reactor would have the exact same effect.

It'd be an easy test with a pair of vise grips. Partially crimp the hose down before the reactor and see how much co2 it can handle. Then do the same thing after the reactor and compare.

Supa Mint

Discussion Starter · #13 · Feb 2, 2017

Supa Mint said:
Ok, I have just started an experiment to test an increase in back pressure. I have used a vise-clamp to pinch/flatten the tubing after the reactor. This is a very unscientific study, since I have no way to know the volume reduction or pressure increase (if any). But if the drop checker indicates an increase in CO2, then I can conclude that my cannister filter can handle some back pressure; and that dissolved CO2 is increased with back pressure.

Surprising results from my first back pressure experiment: The sound of the gas/liquid layer within the reactor disappeared; and I still did not observe any CO2 bubbles in the aquarium. However, there was no observable difference in the color of the drop checker!

So I'm still completely baffled as to where my CO2 is going!

I believe that the drop checker is performing correctly, since I could get it turn yellow when using an in-line diffuser (with lots of micro-bubbles); and because it also turns yellow when exposed to air (during water changes).

As stated previously, I do not know where I could be losing CO2 - no bubbles in tank, minimal surface agitation, and no observable CO2 leaks.

For next steps, I can think of trying the following:
1. Reduce adjustable flow rate of canister filter - while this may increase dwell time, I wonder if the gas/liquid layer in the reactor will become larger.
2. Increase the CO2 delivery rate - at >10bps, and a gas/liquid layer forming in the reactor, I feel that I'm already at an excessive CO2 delivery rate for my water flow rate; however, I'm running out of ideas.
3. Install inline diffuser before the reactor (and capping CO2 inlet port of reactor) - thinking that delivering micro-CO2 bubbles (rather than large bubbles) to the reactor may help with dissolving the CO2.

Any thoughts or suggestions would be very welcome!

- Erick

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burr740

· #14 · Feb 2, 2017

I'd toss the drop checker, they're only rough guess under the best of circumstances. Too much room for error.

Better to do a relative PH test between degassed tank water and the tank with the co2 on. There should be a full 1.0 drop, minimum, preferably by the time the lights come on, or shortly thereafter.

You'll need a digital PH pen to do this, cant use drop tests or strips. They're about 15-20 bucks on amazon, and you'll need some 7.0 calibration solution. It's the best investment you can make at this point.

Side note:
Here's an interesting vid where a guy with a cerges fixed a problem by adding more pressure. The pressure discussion starts around the 3 min mark

https://www.youtube.com/watch?v=Itj-qxlKmIo

natemcnutty

· #15 · Feb 2, 2017

Have you tried reaching out to Colin about this yet? I'm building my own reactor this weekend powered by a 2215. I'll see if I can replicate your issue and play with length and diameter to see what makes a difference

Sent from my Nexus 6 using Tapatalk

NickRummy

· #16 · Feb 3, 2017

I'm going to chime in just because we have similar setups and I'm just getting back into this and I've noticed a few things on my setup recently. I'm running a 29G with a Marineland C-220 (220gph) and a Koralia 240 powerhead on during the day.

What pressure is your CO2 being injected at? I've attached a photo of my setup. When I first built a few years ago (I didn't use it for a while and just started it back up a few days ago). I added a pressure gauge to the top of my reactor in hopes of seeing pressure but like noted in this thread there isn't enough to measure on a 0-100 scale. Wondering if there might be other gauges out there that could? I have a valve on the output of my reactor but I run it wide open. I haven't had any issues with bubbles getting into the display tank yet.

Could it be possible there is oxygen in the top of the reactor and it's just sitting there? I added a valve into the top of my reactor (see the tube coming off it) so that when I do cleaning and refill with water I can purge any air out.

One thing I noticed yesterday was that I would randomly get the air noise in the reactor too. I can only run my CO2 at around 20psi (Red Sea regulator) right now and I'm noticing that water actually goes into the CO2 tube and then eventually the CO2 pushes back into the reactor. I'm not running a backflow valve though so I'm sure that's half the reason. I have a GLA system coming I'm swapping to. I just added a drop checker the other day and it's still showing low CO2. I don't have many plants and I'm trying to start out slow so I'm running around 1.5bps and slowly bringing it up until I get what I want.

I also have an RKE system coming with a PH probe that I'm hoping will help with CO2 amounts.

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PlantedRich

· #17 · Feb 3, 2017

Another thought might be that the reactor is okay. Colin has a habit of building/selling good stuff so I would be reluctant to mod it until I really understood it totally.
No idea on how you operate, so I don't want this to sound like pointing a finger? But tis there a chance that the way you are restating the canister needs some change. Possible that you need to tilt the reactor on restarts so that the air is not trapped in it?
I have reactors in a number of different setups and find there is a difference in the way they need to operate. When the reactor sets on the floor next to the canister, I need to leave it loose so that I can swing the base up to drain the air out to get a good restart after filter cleaning.
Any possibility that much of the bubbles and noise in not from CO2, but simple trapped air? Maybe an easy , low level test would be to tip the base of the reactor so that any trapped air will pass through and see how it changes things?
I'm told by high level thinkers that this doesn't happen but then they are not at my tank when they say that~!

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NickRummy

· #18 · Feb 3, 2017

Found this for a gauge that should read the pressure, but it's not cheap. Don't think you really get anything out of know the pressure either since it's so minimal. Makes me wonder if the pressure would show up though. haha

https://www.amazon.com/Kodiak-Contr...1486134410&sr=8-5&keywords=low+pressure+gauge

RobnSonji

· #19 · Feb 3, 2017

burr740 said:
I'd toss the drop checker, they're only rough guess under the best of circumstances. Too much room for error.

Better to do a relative PH test between degassed tank water and the tank with the co2 on. There should be a full 1.0 drop, minimum, preferably by the time the lights come on, or shortly thereafter.

You'll need a digital PH pen to do this, cant use drop tests or strips. They're about 15-20 bucks on amazon, and you'll need some 7.0 calibration solution. It's the best investment you can make at this point.

Side note:
Here's an interesting vid where a guy with a cerges fixed a problem by adding more pressure. The pressure discussion starts around the 3 min mark

https://www.youtube.com/watch?v=Itj-qxlKmIo

After watching the video.... It looks like increasing the pressure on the inlet side did help?
He increased pressure on the in side by using 2 canisters plumbed together. Am I understanding that correctly?
If you dont have enough water flow to keep the bubbles churning they build up at the top to form one large bubble that does not have enough contact with the water to dissolve.

It leaves me with the impression that you need enough water flow to keep the bubbles churning and not building up at the top.....and....enough dwell time for the bubbles to dissolve.

PlantedRich

· #20 · Feb 3, 2017

When thinking further, we all have a gauge on our reactor pressure but just don't think of it that way. We use the reg to set the working pressure going into the reactor and the pressure is the same at the reg as at the reactor. So to find what pressure is in that line, we can watch the bubble count and when we turn the working pressure down to the point that bubbles neither enter nor water come out, we are close to the reactor pressure?
Critics might point out that this ignores the "friction" of the tubing, etc., etc. but I'm not speaking rocket science.

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