My first DIY reactor... How did I do?

[TRyan]

I didn't catch what size of tank this is in?

I have a 44 gallon tank and when I used a bubble counter, it was more like 4-5 bubbles per second? to reach 1 ph drop. It's really hard to count that fast.

 

[TRyan]

How big is the aquarium. The only aquarium I have that comes close to the CO2 levels I want at the 1 BPS rule is my 7 gallon tank. My 25 gallon is probably 3 BPS at least and my larger aquariums have BPS rates that you can't count.

Haha, I think we posted at the same exact time

 

[markn2025]

How big is the aquarium. The only aquarium I have that comes close to the CO2 levels I want at the 1 BPS rule is my 7 gallon tank. My 25 gallon is probably 3 BPS at least and my larger aquariums have BPS rates that you can't count.

It's 240 litre, I'll up it!

 

[markn2025]

@Yugang @stonedboss @Art or anyone who knows about this. Can someone help? This is my setup on a 240L tank but it doesnt seem right. Fluval fx4 running at 90% with bypass about 60% closed. Drop checker is completely blue. My second day running co2 and it's been on for 3 hours today so far. No bubbles at all out of the filter and no leaks.

What should I change or do? What looks normal?

 

[Koan]

What is the surface area of your tank, and what are the dimensions of your reactor? Is this reactor sized accurately to be safe running in "overflow mode"?

Overflow mode means that the maximum surface area inside your reactor, ie the biggest bubble of gas you can create before it starts to purge out the exit valve, is sized to your size of tank without exceeding that safe level of CO2.

If the maximum size of your reactor gas bubble is too big for the size of your tank, so that that max level of CO2 would exceed a safe level for your tank, then you will need to use bps to create a smaller-than-maximum gas pocket.

The co2 doesn't seem to be making a large bubble it's been on for 4 hours now

Looking at this video, it appears your flow through the reactor is way too fast, and your injection of CO2 is too slow. The CO2 you are injecting is getting sucked out the far end of the reactor before it can back up and create a gas pocket.

Remember that a drop checker color change has at least a 2-hour lag time and is not a real-time indicator of your co2. It is a very good idea to have a Hanna CO2 test on hand to keep track of the CO2 levels in your tank.

If you have fish in the tank, keep an air stone handy while you are tuning this. If you overshoot and the fish become stressed you want to be able to blow the extra CO2 off.

To set up and tune this reactor, you will need to :

1) First, tune the flow through the reactor to just a very gentle flow, which means the majority of the FX pressure is likely to be going through your bypass.

If your reactor is not filled with completely with water at this stage, that means that any pocket that you are seeing in there is air, not CO2.

If the reactor is filled completely with water at this stage, it will be a little easier to visually tune.

2) Second, turn up your CO2 injection into the reactor, and watch it until you see a big gas pocket forming. Don't worry about bps right now, turn it way up. You are purging out the oxygen from any preexisting reactor pocket and creating a CO2 gas pocket.


3) Once you see a gas pocket form, turn the BPS back down to a level that maintains the pocket without expanding it further. Watch your livestock carefully for the next half an hour or so, then check the pH drop in your tank or check the CO2 with a Hanna CO2 tester, to evaluate the level of CO2 you are injecting at this BPS / at this pocket size.

 

[markn2025]

What is the surface area of your tank, and what are the dimensions of your reactor? Is this reactor sized accurately to be safe and running in "overflow mode"?

Overflow mode means that the maximum surface area inside your reactor, ie the biggest bubble of gas you can create before it starts to purge out the exit valve, is sized to your size of tank without exceeding that safe level of CO2.

If the maximum size of your reactor gas bubble is too big for the size of your tank, so that that max level of CO2 would exceed a safe level for your tank, then you will need to use bps to create a smaller-than-maximum gas pocket.



Looking at this video, it appears your flow through the reactor is way too fast, and your injection of CO2 is too slow. The CO2 you are injecting is getting sucked out the far end of the reactor before it can back up and create a gas pocket.

Remember that a drop checker color change has at least a 2-hour lag time and is not a real-time indicator of your co2. It is a very good idea to have a Hanna CO2 test on hand to keep track of the CO2 levels in your tank.

If you have fish in the tank, keep an air stone handy while you are tuning this. If you overshoot and the fish become stressed you want to be able to blow the extra CO2 off.

To set up and tune this reactor, you will need to :

1) First, tune the flow through the reactor to just a very gentle flow, which means the majority of the FX pressure is likely to be going through your bypass.

If your reactor is not filled with completely with water at this stage, that means that any pocket that you are seeing in there is air, not CO2.

If the reactor is filled completely with water at this stage, it will be a little easier to visually tune.

2) Second, turn up your CO2 injection into the reactor, and watch it until you see a big gas pocket forming. Don't worry about bps right now, turn it way up. You are purging out the oxygen from any preexisting reactor pocket and creating a CO2 gas pocket.

View attachment 13361
3) Once you see a gas pocket form, turn the BPS back down to a level that maintains the pocket without expanding it further. Watch your livestock carefully for the next half an hour or so, then check the pH drop in your tank or check the CO2 with a Hanna CO2 tester, to evaluate the level of CO2 you are injecting at this BPS / at this pocket size.

Thank you so much for the detailed reply. My tank is 120x40cm and my reactor is 50mm OD and 50cm long. I sized it to less than a 1.5 ph drop in overflow mode.

I turned the flow down significantly, moving the bypass to about 70% open and I started to see more of a bubble, my co2 is off for the day now so will check it again tomorrow morning but it definitely made an immediate positive impact. Hopefully that was my issue, I'll take another look at it tomorrow and assess over the day. How long before lights on roughly should I have it turn on?

 

[Koan]

How long before lights on roughly should I have it turn on

Here's a good discussion on that

Resource Thread 'Hanna CO2 Test Kit: My experience so far (and why you're probably not starting CO2 injection early enough)!'

Mar 27, 2025

The 2hrAquarist legend Dennis Wong tested the Hanna Test Kit vs a $3,000+ CO2 testing device and found accurate results in low kH aquasoil based tanks when compared. $30 for CO2 readings vs $3,000+!

It's a simple kit that comes with simple instructions, two differently sized vials for different detection ranges, a titration syringe phenolphthalein indicator, and an NaOH solution of some unknown concentration to titrate with.

For the range of detection on the Hanna CO2 test kit we want (0-50ppm):

• Add 10mL of aquarium water to the small flask. Add 1...

• Naturescapes_Rocco
• co2 co2 measurement hanna injection test kit titration
• Replies: 39
• Forum: Fertilizing and Aquarium Chemistry

• 
• 

 

[markn2025]

Here's a good discussion on that

Resource Thread 'Hanna CO2 Test Kit: My experience so far (and why you're probably not starting CO2 injection early enough)!'

Mar 27, 2025

The 2hrAquarist legend Dennis Wong tested the Hanna Test Kit vs a $3,000+ CO2 testing device and found accurate results in low kH aquasoil based tanks when compared. $30 for CO2 readings vs $3,000+!

It's a simple kit that comes with simple instructions, two differently sized vials for different detection ranges, a titration syringe phenolphthalein indicator, and an NaOH solution of some unknown concentration to titrate with.

For the range of detection on the Hanna CO2 test kit we want (0-50ppm):

• Add 10mL of aquarium water to the small flask. Add 1...

• Naturescapes_Rocco
• co2 co2 measurement hanna injection test kit titration
• Replies: 39
• Forum: Fertilizing and Aquarium Chemistry

• 
• 

A great read.

So, I currently have it to come on 2.5hrs before light on and off 1hr before light off.

Beat case tomorrow I wake up to a blue/green checker at lights on and a stable bubble in the reactor, that gets greener over next few hours. In that case I can just turn the co2 on earlier. I'd rather use that approach than have shed loads of surface agitation and a higher input because I have floaters in the tank that it would destroy.

 

[That Guy Brian]

Here's a good discussion on that

Resource Thread 'Hanna CO2 Test Kit: My experience so far (and why you're probably not starting CO2 injection early enough)!'

Mar 27, 2025

The 2hrAquarist legend Dennis Wong tested the Hanna Test Kit vs a $3,000+ CO2 testing device and found accurate results in low kH aquasoil based tanks when compared. $30 for CO2 readings vs $3,000+!

It's a simple kit that comes with simple instructions, two differently sized vials for different detection ranges, a titration syringe phenolphthalein indicator, and an NaOH solution of some unknown concentration to titrate with.

For the range of detection on the Hanna CO2 test kit we want (0-50ppm):

• Add 10mL of aquarium water to the small flask. Add 1...

• Naturescapes_Rocco
• co2 co2 measurement hanna injection test kit titration
• Replies: 39
• Forum: Fertilizing and Aquarium Chemistry

• 
• 

Wow. Great information. Had to read it twice and I still don't know if I absorbed it all! Thank you!

-B

 

[hamfist]

Some good advice so far. You really don't need much flow at all through the reactor for it to work really nicely. Any hint of too much flow and your CO2 will simply get sucked out through the outlet.
As a comparison, I run a Yugang on a 500 litre tank. Reactor is run on overflow mode. It's hard to be exact but I'm putting in around 6-8 bps to get it just occasionally overflowing with a bubble out to the tank (about once a minute).
Also remember that you are not going to get a reactor 50% full with CO2. Evn with a higher flow of CO2 into the reactor the accumulated CO2 bubble can only extend down to the top of the outlet pipe, which will be around a third of the way down the reactor befiree it overflows into the tank.

 

[Naturescapes_Rocco]

Also remember that you are not going to get a reactor 50% full with CO2. Evn with a higher flow of CO2 into the reactor the accumulated CO2 bubble can only extend down to the top of the outlet pipe, which will be around a third of the way down the reactor befiree it overflows into the tank.

Glad you mentioned this. This is one of my biggest concerns with a lot of these DIY builds that are seeing underpowered reactors lately.

Reactors with an offset exit, like the ARC Acrylic/Stainless reactors, allow not only far more options in terms of decreasing strength, but also will allow the reactor to reach it's max power. It's why I recommend using 1/15th power (or more), instead of 1/17th power, if building a reactor that has a centered exit.

 

[markn2025]

Glad you mentioned this. This is one of my biggest concerns with a lot of these DIY builds that are seeing underpowered reactors lately.

Reactors with an offset exit, like the ARC Acrylic/Stainless reactors, allow not only far more options in terms of decreasing strength, but also will allow the reactor to reach it's max power. It's why I recommend using 1/15th power (or more), instead of 1/17th power, if building a reactor that has a centered exit.

I'm not concerned about being underpowered yet. At this stage I'm simply using it wrong, there was little to no bubble in the reactor all day, I think I was smashing far too much flow through it. I've opened up the bypass so will see how it goes tomorrow but thank you as always

 

[TRyan]

To hit 30ppm C02 in your tank of 63 gallons, you should basically see a steady stream of bubbles in your bubble counter. Too many to count with the naked eye.

The amount you're injecting now might be enough for a 10 gallon tank. Double your injection rate for now, but that likely won't even be enough, though it'll be a good place to start.

 

[Kwyet]

When I set mine up, I turned the bubble count high enough to fill the reactor quickly, then turned it down so there were only a few small bubbles coming out about once a minute. If you already have fish you’ll have to monitor carefully to make sure they’re handling it okay. If the CO2 level gets too high with that method, then control it by setting the reactor to a smaller bubble or by lowering the bps.

 

[markn2025]

I'm at a loss. This is my bps and reactor, my bps is higher than it ever was with my diffuser and my drop checker is still completely blue. There is no bubbles coming out my outputs. Video shows current setup, bypass about 30% closed. Please help feels like a complete waste of time at the moment

 

[hamfist]

When I set mine up, I turned the bubble count high enough to fill the reactor quickly, then turned it down so there were only a few small bubbles coming out about once a minute. If you already have fish you’ll have to monitor carefully to make sure they’re handling it okay. If the CO2 level gets too high with that method, then control it by setting the reactor to a smaller bubble or by lowering the bps.

Yes, well mentioned, this method worked for me very well too. Filling the reactor up to its "overflow point" with a really high bps then turning it down until only occasional "burping" overflow of CO2 into the tank is seen (around once every 1-2 minutes).

 

[Naturescapes_Rocco]

I'm at a loss. This is my bps and reactor, my bps is higher than it ever was with my diffuser and my drop checker is still completely blue. There is no bubbles coming out my outputs. Video shows current setup, bypass about 30% closed. Please help feels like a complete waste of time at the moment

Increase your BPS until you see a change in your drop checker and report back.

Also, what kind of drop checker are you using? In tank, over the rim, etc?

 

[markn2025]

Increase your BPS until you see a change in your drop checker and report back.

Also, what kind of drop checker are you using? In tank, over the rim, etc?

In tank. I've used it for ages with my diffuser before this.

I'm concerned that I don't have enough flow through my reactor the water looks still. God knows, I'll keep trying. Co2 off for the day so will have to be tomorrow

 

[Koan]

the water looks still

Well it does have to move

The CO2 is diffusing across the surface in the reactor, from the gas in the pocket into that body of water in the reactor.

If you want to get to CO2 out of the reactor, and into the tank, then that body of water needs to flow out.. into the tank

 

[markn2025]

Well it does have to move

The CO2 is diffusing across the surface in the reactor, from the gas in the pocket into that body of water in the reactor.

If you want to get to CO2 out of the reactor, and into the tank, then that body of water needs to flow out.. into the tank

Thank you. I've put my bypass to 50% open. It was about 80% open before. Will see how that goes tomorrow.