# CO2 OFF Solenoid & Venturi Diffuser or ON: Constant Flow



## fishstein (Dec 12, 2005)

Currently, I have a 20lb CO2 tank with dual regulator and needle valve feeding into a diffuser placed next to the output of a strong powerhead. It works but is not the most efficient CO2 diffusion method. I’m going to start using a Red Sea 500 venturi diffuser with built in pump to better dissolve CO2 into the water with less waste (the 500 is quite small, an advantage in hiding it and has a built in bubble counter). Also, I find I have to scrub the surface of my stone/ceramic diffuser plate every week to keep the bubbles small. 

I had always thought that using a solenoid to shut off CO2 at night, when the lights are off, would be a good idea, saving CO2 and preventing fish stress from excess CO2 at night. However, I worry about the effects of pH swings, especially on my Tanganyikan fish (planted Tanganyikan tank, 75 gallons). After setting up the Red Sea 500, should I:

1) stick with constant flow 
2) set a timer to shut off the Red Sea 500 when the lights are off to greatly reduce dissolved CO2 or 
3) use a solenoid to save CO2 gas and reduce CO2 in the tank when lights are off? 

Will 2) and 3) cause dangerous pH/CO2 swings? Will keeping the CO2 and Red Sea 500 going at night cause dangerous CO2 buildup?

Note that I have medium to high hardness and a pH around 7.6-8, plus I keep 2.5 cups of aragonite in my XP3 canister filter to buffer (in addition to serving as bio media).

Thanks and Best Regards,

Fishstein


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## Catastrophi (May 23, 2006)

I think you should turn it off at night. Ph swings aren't too too bad.


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## John N. (Dec 11, 2005)

Yes not to worry much about pH swings. You're fish won't die. My fish and shrimp are still kick around with the CO2 going off at night. So no worries.

I would turn off put the Solenoid on a timer to shut it off when the lights go off.

By the way (btw), in the future do not scrub the ceramic disk. A 5 minute dip in bleach will clean it off quickly and produce misty bubbles. Scrubbing will trap the particles in the disk.

-John N.


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## fishstein (Dec 12, 2005)

Thanks John for the bleach tip, will do.

So you would prefer a solenoid over setting the Red Sea 500 venturi diffuser on a timer? When the 500 venturi pump is off, the CO2 simply gasses off in large bubbles straight up the water column, so it's almost as good as shutting off the CO2 with a solenoid. The only difference is that the solenoid would save some CO2 rather than just let it gas off, perhaps allowing the CO2 tank last 2x as long. A solenoid or solenoid + regulator combo (which can be had fairly inexpensively on eBay, I think about $85 + shipping for the combo with bubble counter), is more expensive than the 500 ($34 at That Fish Place) with timer ($6 at That Fish Place).

My only problems with the small Eheim diffuser I have is that 1) it clogs fairly frequently in my hard water chemistry in the tank 2) it's hard to count bubbles because when the stone diffuser clogs slightly, the chamber fills with gas, replacing water, and making bubble counting impossible. Maybe things will improve after a bleach dip, but I don't know how long it can stay clog-free.

Also, would that small Eheim diffuser be able to diffuse as well for a 75 gallon tank as the venturi chamber diffuser on the Red Sea 500?

Has anyone had any experience with the Red Sea 500?

Caught pics of your tanks, great work.


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## hoppycalif (Apr 7, 2005)

I used that eheim diffuser for a few weeks, but quit using it to try a powerhead as a means of chopping up CO2 bubbles into smaller ones. I still have the one I used, if you want a spare. (Postage only). I found I had to soak it in bleach about every two weeks to keep the small bubbles going.

Now I just use a powerhead with a sponge filter and the CO2 tube stuck into the powerhead inlet. It works fine, but I know others recommend using a little airstone or something on the CO2 tube so the powerhead is fed with already small bubbles. I shut off the CO2 at lights out, leaving the powerhead running for water circulation and filtration.


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## fishstein (Dec 12, 2005)

Thanks HoppyCalif,

Using a small airstone (I'd say ceramic, keep 2, so you can soak 1 in bleach every few weeks) to make the bubbles smaller before feeding into your powerhead will make diffusion more efficient. Another option is what I do currently - I have the fine bubbles rising from my Eheim diffuser going right up into the output of a powerful powerhead, which spreads them around the whole tank in a circular current and allows much more contact time for the CO2 to diffuse.

I'll gladly take that spare, I could use it for a friend's newbie tank or for a new smaller tank I'll set up soon. I'll PM you with details. Thanks!


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## John N. (Dec 11, 2005)

fishstein said:


> Another option is what I do currently - I have the fine bubbles rising from my Eheim diffuser going right up into the output of a powerful powerhead, which spreads them around the whole tank in a circular current and allows much more contact time for the CO2 to diffuse.


This is what I do, and it's working out perfectly. Plants are pearling, and the pH drops to where I need it.

There's a poll regarding CO2 24/7 or not in the General discussion subforum APC polls that might give you an idea what people are doing. I prefer to save C02 and use the solenoid to turn it off at night.

Sometimes it helps to place the diffusor in a dark corner away from the light. That will limit how much algae grows on it making a cleaner diffusor for a longer period of time.

-John N.


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## fishstein (Dec 12, 2005)

Hi John,

I like your idea of placing the diffuser in a shaded area - algae has primarily clogged the holes in the Eheim diffuser disk - but that wouldn't allow me to take advantage of the powerhead output in my case. However, this may not matter much, as I may give the Red Sea 500 a whirl - it seems to be what I've been looking for - a very compact, easy to hide and highly efficient venturi powered diffuser that will need much less maintenance - just pulling off any caught vegetation or leaves on the intake of the venturi pump once in a while + cleaning the sintered glass diffuser disk maybe once in 2-3 months, which is located inside the 500 and thus shaded from light). After checking out the design of the 500, I may be inspired to make my own venturi diffuser.

I'm going to add a solenoid, but since I found a reasonably priced solenoid + bubble counter + dual regulator + needle valve all-all-in-one unit and I don't want to fiddle with fitting my own components together, I may just buy that setup and sell my dual regulator + needle valve setup, which is extraordinarily high quality, to a hobbyist that doesn't use solenoids.


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