# [Wet Thumb Forum]-A little help from the engineers and physicists...



## 2la (Feb 3, 2003)

I have a 1-1/2"-diameter CO2 reactor based on James Hofteizer's design hooked inline between the intake and canister of my Rena Filstar XP1 filter, rated at 165gph on the Rena website but at 250gph by most other sites (mostly retailers). The problem I have is with excessive air entrapment in the filter leading to frequent airlocks that occasionally correct themselves but that all too often don't. At these points, I have to do everything short of black magic to burp the air out of the filter and get it going again. This happens probably two or three times a day. Obviously, if I have designs on taking an extended vacation, my fish are in immense danger of noncirculating water. Even IF I weren't away, I'm finding that having to do this several times a day is quite unacceptable. Flow rate has also slowed to a snail's pace lately. Injection rate is about 1 bubble/second, BTW.

I don't know if others have problems with this particular design, but the least I can say right now is that this setup clearly is not right for MY system (sorry, James, I certainly don't mean to besmirch your design) and I'd like to start from scratch with a design based on Ghazanfar's and Tom's reactor (pictures not working in that thread, BTW...any chance they'll be up again?).

My main question is in where the CO2 input should go on the reactor cylinder. Is it a true countercurrent mechanism where the bubbles can be run through at the bottom with the counterflow of the water breaking the bubbles up as they attempt to float upwards? Or is it more a matter of churning the CO2/water interface at the top of the reactor, hence the input for CO2 at the top? I realize most people have the CO2 input towards (perpendicular to water flow) if not at the top (running parallel to water flow), but I'd really like to minimize the risk of airlocking. Have people tried running the CO2 into the reactor more towards the bottom of it (and with any success if so)? I apologize for the long post, but hopefully that made some sense. Any and all help much appreciated.

2la


----------



## 2la (Feb 3, 2003)

I have a 1-1/2"-diameter CO2 reactor based on James Hofteizer's design hooked inline between the intake and canister of my Rena Filstar XP1 filter, rated at 165gph on the Rena website but at 250gph by most other sites (mostly retailers). The problem I have is with excessive air entrapment in the filter leading to frequent airlocks that occasionally correct themselves but that all too often don't. At these points, I have to do everything short of black magic to burp the air out of the filter and get it going again. This happens probably two or three times a day. Obviously, if I have designs on taking an extended vacation, my fish are in immense danger of noncirculating water. Even IF I weren't away, I'm finding that having to do this several times a day is quite unacceptable. Flow rate has also slowed to a snail's pace lately. Injection rate is about 1 bubble/second, BTW.

I don't know if others have problems with this particular design, but the least I can say right now is that this setup clearly is not right for MY system (sorry, James, I certainly don't mean to besmirch your design) and I'd like to start from scratch with a design based on Ghazanfar's and Tom's reactor (pictures not working in that thread, BTW...any chance they'll be up again?).

My main question is in where the CO2 input should go on the reactor cylinder. Is it a true countercurrent mechanism where the bubbles can be run through at the bottom with the counterflow of the water breaking the bubbles up as they attempt to float upwards? Or is it more a matter of churning the CO2/water interface at the top of the reactor, hence the input for CO2 at the top? I realize most people have the CO2 input towards (perpendicular to water flow) if not at the top (running parallel to water flow), but I'd really like to minimize the risk of airlocking. Have people tried running the CO2 into the reactor more towards the bottom of it (and with any success if so)? I apologize for the long post, but hopefully that made some sense. Any and all help much appreciated.

2la


----------



## gsmollin (Feb 3, 2003)

I think your problem is that the reactor has to be on the outlet side of the filter. The water contains a lot of dissolved O2 with CO2 injection. Frequently it's at O2 saturation levels- hence all that pretty pearling. The reactor provides some back-pressure, and with it located on the inlet side of the filter, the filter pump is causing a reduced-pressure between the reactor and the filter inlet. The water is already saturated with O2, and the reduced pressure is causing the water to out-gas O2, much as it does after a water change. The O2 is collecting in your filter pump, and causing cavitation.

At least that's what I think.

The solution is to put the reactor on the outlet side. Now the back-pressure causes the filter to run at a higher pressure, not lesser, and out-gassing should be reduced.


----------



## Rex Grigg (Jan 22, 2004)

I would agree with gsmollin here. I have two DIY reactors, one on a XP2 and the other on a XP3. On the output side of the filter no problems. On the input side problems. Not so much with lower light tanks, but on the 4 wpg 55 gallon and the XP3 I have had problems.

Moderator










American by birth, Marine by the grace of God! This post spell checked with IESpell available at http://www.iespell.com

See my Profile for tank details.


----------



## Jon Mulzer (Mar 9, 2003)

Not trying to hijack a thread here, but what is the actual rating of the XP series? I have been impressed with the XP's but didn't think they made one that wouldn't turn my tank into a whirlpool. If they are actually 165 gph that would be perfect.


----------



## 2la (Feb 3, 2003)

I guess I've always been under the assumption that the reactor goes on the intake side, at least that was the impression I got from Ghazanfar's DIY thread. Or is there more than one way to skin a cat? I guess I'm confused as to what factors are at play that would make one person's system work flawlessly while another similar setup (i.e., mine) hiccups all the time.

In any case, if I put the reactor inline on the output side, it still needs to upright, is that correct? I.e., the water should flow from top to bottom and the CO2 would enter from the top?

Thanks for the help, guys.

Rex, did you decide to go with the metal halide for the new betta tank?


----------



## Jon Mulzer (Mar 9, 2003)

It can be set-up either way, and both have their pros and cons. If you are running a reactor that is designed like James' then it pretty much has to be on the outlet side of the filter. With ones set up on the intake side you run the risk of clogging it with debris (run a pre-filter) and also if it is not designed properly you can get negative pressure which will cause the outgassing if you are near or above 100% O2 saturation. But if it is done properly you really shouldn't have to worry about it. What are you using to disrupt the flow inside of the reactor? If the bio balls fit too tightly they will choke off the flow causing the problems you are having.

If you put it on the outlet of the filter and there is a restriction at the reactor you will reduce the flow of your filter. But that reduction will cause positive pressure in the impeller housing which will reduce the outgassing problem. The plus side of this design is that you are running filtered water through the reactor and don't have to worry about clogging.

Either one if properly designed will be more than adequate, you just have to be careful in the design and implementation to avoid the problems. In either case the flow of water has to be counter-current to the bubbles, or top to bottom. I am not sure about the ideal spot to inject CO2, different designs do it different ways and no one really says much about the benefits or detriments of each. As long as the current is not strong enough to simply push the bubbles out the bottom I don't think it matters all that much. The flow through the reactor should be at a much lower velocity than through the hose (because the reactor is a much larger diameter) so as long as there is turbulent waterflow from whatever media you place inside it should be ok.

Just my opinion and I have been wrong many times before.


----------



## ekim (Jan 31, 2004)

2la, I had a similare problem, I made a longer reactor and that solved the problem! Some of us put the reactor on the input side because gravity will help pull the water through, and it minimises the amount of head you filter will have to pump. I tried the reactor on the output side but my filter (fluval 304) pretty much stoped (10gallons / hour). The difference in head pretty much was doubled on the output side! 
Here is a pic of 1 of mine made from a large gravel vacum tube. It's 2" in diameter and 18" tall.


----------



## Rex Grigg (Jan 22, 2004)

I decided to go with the 175 watt MH light for the 5.5 gallon Betta tank. We all know that smaller tanks take more light.









Moderator










American by birth, Marine by the grace of God! This post spell checked with IESpell available at http://www.iespell.com

See my Profile for tank details.


----------



## JamesHoftiezer (Feb 2, 2003)

Ditto to all of the above.

The problems are reduced in almost all cases if you use the outlet from the pumps. Otherwise;
1) you have dirt collecting in the reactor
2) certain filters will burp and hiccup
3) you may actually outgas the CO2/O2 in the impeller if they are near saturation points

Downside is that it may reduce flow, but prior planning can aid this or an inline pump can be added afterwards. In my setup, I saw no indication of flow reduction on my 2028. I have an inline pump but have never needed to install it.

The CO2 can be added in the bottom or the top, but must rise into the flow of water (just trying to say the same thing a different way). In my design I inject at the top into a 90 degree fitting in the hope that the added turbulance in the knuckle will increase absorption at the top.

In reactors you count both the turbulence in the air pocket and the collision of CO2 bubbles into the bioballs to absorb the CO2. If neither hapened then it would be a diffuser instead of a reactor.

*James Hoftiezer

Tank Journal - Aquascape ( Latest / Archive )
Tank Journal - Parts and Construction ( Latest / Archive )*


----------



## JamesHoftiezer (Feb 2, 2003)

Also ....
There is a difference between the rated flowrate and the service flowrate on a filter.

A rated flowrate is before the media and everything else is installed. It really is the rating of the pump if nothing else was attached.

The service rating is for the filter with all the media in it and assuming 0ft on the pumphead.

You could have a 300gph pump, but once you fill the baskets with media and force the water up 5ft to the top of your tank it may only really be able to deliver 200gph.

The service rating is what youreallywant to see, but considering the truth in advertising whey will show the rated flowrate since it is higher.

Eheim is the best at distinguishing the two and could be interpolated for other filters.

*James Hoftiezer

Tank Journal - Aquascape ( Latest / Archive )
Tank Journal - Parts and Construction ( Latest / Archive )*


----------



## Doomer (Feb 2, 2003)

> quote:
> 
> I decided to go with the 175 watt MH light for the 5.5 gallon Betta tank. We all know that smaller tanks take more light.


Hope you bought the fish some shades.


----------



## 2la (Feb 3, 2003)

Hey everyone, thanks immensely for the replies. James, your reactor works like a charm now that it's on the output side of the filter. I think the supersaturation issue was the biggest factor, though it may also be a Filstar thing as Rex's similar experiences suggest. Everything's up and running smoothly, and now the only agitation I feel is when I place my hand on the reactor.


----------



## farm41 (Feb 1, 2003)

I see some people have a misconception of 'feet of head'. If you have a sump 5' below your tank, you would have 5' of head plus the additional 'feet of head' for any restriction in the plumbing setup. But in a closed system where there is water coming down to the cannister it is cancelling out the push back up. The only feet of head is in the restriction of the plumbing setup. An easy little experiment to see if this is so is to turn the water off. If it runs back down the hose 5', you have 5' feet of head.

Matt
If you're not making any mistakes, you're not doing anything


----------



## ekim (Jan 31, 2004)

Hey farm41, was your comment directed at me?
Did I explain how to measure head?
I don't see a misconception!


----------



## farm41 (Feb 1, 2003)

> quote:
> 
> Originally posted by ekim:
> The difference in head pretty much was doubled on the output side!


Maybe I'm the one that is confused.

Matt
If you're not making any mistakes, you're not doing anything


----------



## ekim (Jan 31, 2004)

It's hard to explain, 
when I put the reactor on the output side the filter, the filter had to pump the water up about 1' to the top of the reactor, then once the water was at the bottom of the reactor it had to be pumped up 5' to the tank. There was a lot more "power" needed to get the water back into the tank. Through all my plumbing the head needed was almost double.
It was obvious that the head increased because the filter would not really pump the water back into the tank, maybe 10 gallons an hour!

This was just my experience with a reactor on the output side of a fluval 304 canister. I'm sure all the filters handle it differently. But the head needed will increase with the reactor on the output side!


----------



## farm41 (Feb 1, 2003)

EKIM, I got it now, you have increased the resistance of the flow on the side with the reactor. 

Something to be aware of though, is that most pump manufacturers recommend is not to restrict the suction side of the pump, if you need to restrict something, always do it on the output side. It appears from what you are saying that your reactor is restricting flow. Restricting flow on the intake side can cause cavitation. Cavitation is very hard on impellors. 

It really has nothing to do with the water going up and down, but more likely resistance in the lines and fittings.

Matt
If you're not making any mistakes, you're not doing anything


----------



## Moe (Feb 1, 2003)

I run mine on the inlet side of an EHEIM 2213 (116gph)
reactor is 2"x14" no problems

Moe


----------



## gsmollin (Feb 3, 2003)

Ok, now I understand why people claim that putting the reactor in the outlet reduces the flowrate.

It's because in the outlet, the plumbing has two 180 degree turns in the tubing. Turns always cause reduction of flowrate, or pressure loss.

With the reactor in the inlet side, the water comes in the top, and goes out the bottom, to the cannister.

With the reactor in the outlet side, the water has to go to the top of the rector, through a 180 degree fitting, down through the reactor,then out through another 180 degree fitting, then back up to the outlet of the filter. The two 180 degree bends mean the water has gone through a tight little circle. There is quite a bit if pressure drop in that.

The simplest mitigation is a larger diameter circle. The tubing should be held to a couple of feet diameter to minimize back pressure. The tubing should also be increased in diameter. If you are running 5/8 tubing, then increase it to 3/4, or 7/8 diameter. Use straight fittings to the reactor. 

I have a UV unit in the outlet of my Magnum 350, and noticed no significant loss in flowrate, but the tubing loops around to and from the UV with large diameter turns.


----------



## ekim (Jan 31, 2004)

farm41, 
so what your saying is it's "increased the resistance", right? I don't think it's all due to the added resistance.... I bet if I took the output that feeds the water back into the tank and lowered it 2' there would be no problem with the flow rate! That would prove it's not resistance, right? Since there is the same amount of tubing the water has to run through!

gsmollin, 
I understand what you are trying to say about too many sharp turn fittings everywhere, but I only had 1-90 degree fitting, the rest of the direction changes were made by bending the tubing in large diameter curves!

Anyhow there is many ways to power our reactors!
I was just sharing my experience with 2la.
Running the reactor on the output side does not work when powered with my filter "fluval" on my setup! It works great with no problems on the input side though! I have no intent on changing the orientation of the reactor since it works with no problems!

Thanks


----------



## gsmollin (Feb 3, 2003)

ekim:

I wasn't addressing you. If your setup works, don't change it. My setup works with the UV on the outlet, and I'm not chnaging it either. 

Otherwise, a booster pump may be necessary.Some of the filter pumps may be pretty wimpy, and adding reactor back-pressure may stall them. Depending on the pump design, there is a difference between inlet-side restriction and outlet-side restriction. Its not obvious from looking at the pump, either. If it doesn't work on the outlet, then it doesn't work, so add a pump, or make up a separate pumped loop. These problems are part of the reason why I like my Magnum 350, even though its cannister is too small for the pump capacity.


----------



## farm41 (Feb 1, 2003)

You have it partially right, it's not *all due* to increased resistance. But resistance can be calulated as feet of head.

Dropping the output creates a siphon, doesn't it?.

Matt
If you're not making any mistakes, you're not doing anything


----------



## Momotaro (Feb 17, 2004)

I have a question that I posted on an earlier thread, but it seems to fit into this thread much better. I believe I just read about increasing the hose diameter on the output of a canister filter fitted with a CO2 reactor on the output side to reduce pressure loss. Wouldn't decreasing the hose diameter prevent pressure loss? I am obviously (and typically!) confused. Here is my situation posted on an earlier thread. I have an Eheim 2126 and am going to install an AB1000 reactor into the output of the cannister. Now to do this I will have to _REDUCE_ the outflow tube from 16/22mm to 12/16mm flow into the reactor and then _increase_ from 12/16mm to 16/22mm and enter the aquarium. I felt that this would accomodate the decreases and increases in outflow pressure. Am I wrong? After reading your posts I am afraid I am on the road to trouble.
Mike


----------



## gsmollin (Feb 3, 2003)

Since I wrote that I'll respond.

The back pressure of the hose is a direct function of the flowrate, and an inverse function of the hose cross-sectional area. So the larger the cross-sectional area, the lesser the back pressure, for a given flowrate. You should be running at least the recommended diameter of hose. NEVER go to a smaller size hose. When adding appliances into the system, which add back pressure of their own, consider increasing the diameter of the hose. Reducing fittings are another source of back pressure, so consider refitting the reactor with full-size fittings.


----------



## anonapersona (Mar 11, 2004)

Question -- with a large diameter in-line reactor on the outflow of the filter and resulting low velocity, won't you expect more difficulty getting the gas to dissolve into solution? On the filter outlet you've lost the chopping action of the impeller as well as the mechanical action of going through the filter media.

Perhaps a sintered glass airstone inside the reactor could help.


----------



## farm41 (Feb 1, 2003)

At any given flow rate, a decrease in diameter of tubing will increase the velocity, which will increase friction which equals flow loss. 

An increase in tubing size has the opposite effect. Reduced velocity and reduced friction which will equal reduced flow loss.

Matt
If you're not making any mistakes, you're not doing anything


----------



## Momotaro (Feb 17, 2004)

The increase in tubing size also be an increase in surface area within the tubing. Wouldn't that also result in an increase in friction and result in a reduction in flow? Seems like anyway you look at it, it's a wash. The rate of flow will always reduce. You would think that the most dramatic reduction of flow would occur in the reactor itself.


----------



## farm41 (Feb 1, 2003)

Not at all. Doubling the tubing size will increase the capacity for flow by four times. 

I think will see what I mean if you take that to extremes. 1/8" tubing versus 1" tubing. What do you think will carry more water at 10 psi?

Matt
If you're not making any mistakes, you're not doing anything


----------



## gsmollin (Feb 3, 2003)

Momotaro,

You're thinking is correct, but you didn't finish. The wall surface area increases as 2 X pi X radius of the tubing. The cross-sectional area increases as pi X pi X radius of the tubing. So the back pressure can go down with increasing tubing sizes.

In the reactor, there is a lot of surface area added, on purpose, to force the water to flow in eddies; to become turbulent. This causes a great deal of back pressure, and it can certainly cause a pump to stall.


----------



## Momotaro (Feb 17, 2004)

Understood (I think). I posed my reactor and hose reduction question to the people at Eheim directly. Here is their response to _my particular_ case:


> quote:
> 
> You won't stress your 2126 by doing this( the impeller will always turn at the same RPM), however you might encounter a reduced flow rate at the end of the cycle. You might try to put the reactor before and after the filter to find the better flow rate.


I wanted to be sure I got it right so I asked again:


> quote:
> 
> That's correct you can reduce the intake or the output to fit the CO2 reactor. The only thing that can happen with this kind of set up is that you will have a slower water flow.


That confirms the reduced flow discussion, and contradicts not using smaller tubing for the reactor. However, despite the OK from Eheim, I do agree with gsmollin. So much so that I gave up on the AB1000 and went with a different reactor.One that was compatable with the Eheim's hosing. This reactor's recommended flow rate is 100-180gph as compared to the AB1000's 250gph. That would be more in keeping with the Eheim's filter circulation of 172gph (pump output 251gph). I think this will prevent the reduction in the rate of flow in my aquarium. Any comments???

Mike


----------



## 2la (Feb 3, 2003)

> quote:
> 
> The cross-sectional area increases as pi X pi X radius of the tubing.


This is nitpicky, I know, but it's the radius that's squared rather than pi.



> quote:
> 
> Question -- with a large diameter in-line reactor on the outflow of the filter and resulting low velocity, won't you expect more difficulty getting the gas to dissolve into solution? On the filter outlet you've lost the chopping action of the impeller as well as the mechanical action of going through the filter media.


This is what I was thinking before I had a chance to see it in practice. NO bubbles escape the reactor! The flow is reduced such that a gas-water interface is created and the incoming flow agitates the surface, facilitating complete dissolution of CO2 into the water. I couldn't find any clear PVC to use so I can't say how much of the reactor is filled with fluid or water. Perhaps someone with a clear reactor can enlighten us.


----------



## imported_aspen (Feb 20, 2003)

>>'I bet if I took the output that feeds the water back into the tank and lowered it 2' there would be no problem with the flow rate!'

try it. it won't make a difference. head is not at issue, when discussing a closed flow from the same body of water. f/i, if what you are saying was true, then if you put a 100 foot hose in the ocean, and the bottom was 100' down and the other end was near the surface, would water flow out either end? nope. head IS at issue when discussing a syphon. the difference in head from the top of the water and the end of the syphon WILL create a positive pressure, and water will flow. generally though, we talk about head as impeding flow, because we discuss it in terms of how much head a pump will pump against. but it works the same way.

only if there was a negative or positive pressure would water flow. when the ends are in the same body of water, head is not at issue as is the case when discussing a filter feeding in and out of the same body of water.

the thing is, though, that impeding flow on the intake side of a filter, can cause air to suck through the seals of the filter, drying them out. however, if you impede the output side, then the seals will remain wet, and not leak. this is the most important thing to remember when impeding flow on a fishtank filter. 

this is easily shown, if you have an inlet and an outlet valve. close the inlet valve, and air will seemilgly come from no-where (out of solution maybe??). nope, but it is really only that the seals are not designed to seal dry, only wet.

obviously bends will impede the flow, due to increased resistance.

rick


----------



## gsmollin (Feb 3, 2003)

That was an intentional error, to see if anybody was paying attention. Only 2la found the error, so 2la gets the Gold Star Forum Award. Congratulations! The rest of you will just have to keep trying!


----------



## Momotaro (Feb 17, 2004)

Come on gsmollin.. "I meant to do that"







What a great thread!! I know am enjoying it!!


----------

