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Hank Junior 10-03-2020 10:33 PM

CO2 Diffuser
Got a problem with a CO2 diffuser I bought, won't mention the brand but its Chinese and was not cheap, made of glass. Every 2-3 days it fills completely with water (begins filling when the CO2 is off at night) which stops it working. I haven't had an aquarium for 20 years but I don't remember my last diffuser having this problem.

As I don't have a non-return valve in the CO2 line (I should have fitted one) I not only have to remove it and suck the water out every 2 days, but also the line which as it is connected to a tank does not empty of water easily. The bubble counter above the solenoid has a non-return valve, so the solenoid is safe, but that is not the problem.

Its pretty annoying. Currently have removed the diffuser and have the large gas bubbles pooling below a shelf in the tank, so at least the gas sits in the tank water without escaping. Its not ideal.

Should a diffuser fill with water? With the supply off there seems to be a pressure drop which allows water in. Not clear to me why there is a pressure drop? I have soapy water tested my entire CO2 supply (that was a real pain but a necessary one) so I know there are no leaks. Does gas leak through the tubing slowly overnight? I am using common air tube.

Maybe the pressure escapes via the gas-water interface at the diffuser, causing a pressure drop (as gas pressure goes to atmospheric), but how would that let water in - how can the gas be replaced by water? Doesn't make sense to me. If water is flowing into the gas line surely the gas must be leaving somehow?

Thanks for any ideas. I am thinking of buying another diffuser and fitting a non-return valve in the line next to the diffuser to ensure my gas line does not back fill with water.

Hank Junior 10-03-2020 11:17 PM

Re: CO2 Diffuser
Actually there is only one part of my CO2 system I haven't leak tested, it just occured to me, its the gas line from the bubble counter which is attached near the CO2 tank. Its brand new standard air line Aquael 4/6mm, aquariums only 3 wks old, so I never suspected a leak there. I should block the end of the gas line, put the gas line in a bucket of water, and see if any gas leaks out under pressure.

I have noticed that now I have no diffuser fitted (just the end of the gas line under the water in the aquarium), that the moment I turn off the gas, it back fills with water about 30cm within 5-10 minutes - it fills with water very quickly. Is this normal? My entire gas line (air tubing) is 1.5m long from the CO2 reservoir to my aquarium.

Any thoughts would be appreciated. Unfortunately the store I bought my gear from is not very helpful. Asking them questions seems to annoy them. I won't be shopping there anymore. The guy only seems to talk to you when you wave a credit card in front of him!

mistergreen 10-04-2020 06:16 AM

Re: CO2 Diffuser
Is there a check valve from the co2 out to the diffuser?
It shouldn’t fill up with water.

Hank Junior 10-04-2020 11:32 AM

Re: CO2 Diffuser
No. There is one in-built to the bubble counter to protect the solenoid, but between the bubble counter (attached to my CO2 cylinder) and my aquarium, the 1.5m of tubing, there is none.

Where do you normally fit one? Is straight next to the diffuser what people do? Will that prevent the diffuser from filling with water? I can see how it would stop the tubing from backfilling with water, but not clear to me how to stop the diffuser from filling with water. I can imagine that it would fill alot less if I fitted one next to the diffuser.

mistergreen 10-04-2020 01:18 PM

Re: CO2 Diffuser
I think you have a faulty diffuser. See if you can return it.

Hank Junior 10-04-2020 04:31 PM

Re: CO2 Diffuser
Thankyou. Will fit a second diffuser I have today and see if that does the same. Just spoke to the store I bought it from and they tell me that its normal to have a diffuser back fill with water, but I explained to him that yes it does work with water, but once it becomes completely filled (no air gap below the ceramic diffuser material) when there is only water there in the diffuser 100%, no gas, and the gas is way back up the gas line, it stops working completely. I have noticed that when it gets partially filled with water it does not work as well as when it is newly fitted, without any liquid inside. They recommend a check-valve, but the store doesn't fit it right at the diffuser and tells me there should be no problems. Unfortunately I won't be near an aquarium store for a while, so will have to get by without a check valve.

As I have not had an aquarium/diffuser for 20 years, I can't remember exactly, but my old Dupla one never had to be cleaned or messed with. I just fitted it once and maybe gave it a clean every once in a while, never remember it having water inside, or if it did, it never stopped working. I am running at low pressure (1 CO2 bubble per 2 seconds, which may be part of the problem). Store owner tells me he runs his at 1 bubble per second. Manufacturer recommends 3-5 bubbles per second, but I have only a 26L tank so am trying to conserve CO2. Might try some higher pressure and see if that helps with the problem.

Thanks for your help.

Hank Junior 10-04-2020 04:34 PM

Re: CO2 Diffuser
Incidentally, though I have noticed the manufacturers recommend a minimum pressure of 30psi (2 atmospheres) and they warn that a diffuser may not work at too low a pressure - my diffuser does work perfectly at 1 bubble per 2 seconds, when it is clear of water, or partially filled with water. Have had it working as low as 1 bubble per 5 seconds, so I can't see how that is the cause of the problem I have. At any pressure I suspect that when I switch off the CO2, the water will start back filling the diffuser and tubing.

Hank Junior 10-04-2020 11:17 PM

Re: CO2 Diffuser
I am pretty sure I have found the problem - it was a leak from the top of my bubble counter attached to my CO2 valves, guages, solenoid and cylinder. It was initially leaking when I first installed it (hence why I did a complete soapy water test weeks ago where I tested all the fittings for leaks - there were none). Moving the tank around must have broken the seal at the top of the bubble counter - its a dodgy bubble counter.

I have learnt a simple trick to test a CO2 supply tubing once you are satisfied all your gas cyclinder fittings aren't leaking. You simply put the end of your supply line under water in the aquarium (no diffuser attached) and watch the bubble count. It should be identical to the bubble counter - I noticed yesterday that it was much lower coming out of the tube. Today I took apart the bubble counter 'again' (its been a few times :j), noticed that the top of the counter has no o-ring. Its just plastic on metal. That doesn't look right, will have to fit my own o-ring soon. Put vaseline again on the thread and the top of the plastic bubble counter cylinder where it meets the metal (where I intend to put an oring soon).

And the diffuser is working better than it ever has. At 1 bubble per 3-5 seconds I have a cascade of miniature bubbles now. I suspect I am going to see less backflow now even without a check valve fitted in the line. Seems not having a check valve is a good indication of the health of your CO2 supply. Heaps of back flow means you have a leak. The check valve inbuilt in the bubble counter is the most important one but I will fit a check valve in the line asap as well.

I noticed today that the back flow problem really only became a major issue this last week. The diffuser worked OK for the first 2 weeks, even if it did partially fill with water.

Don't buy cheap CO2 setups people - ain't worth it - you will spend weeks sorting it out, redesigning it. It didn't look cheap, and the price was pretty high, but seems the bubble counter is doddgy as hell. Its made in Taiwan, not China, I was wrong on that point. The diffuser has good reviews on Amazon, so I don't think its the diffuser anymore.

Today, before sorting it all out, I fitted the diffuser that came with the CO2 setup (I had upgraded the diffuser and never used it before). Its a joke. The diffuser surface feels smooth as rubber, not the coarse grain you would expect. After waiting 3-4 hours for the gas to come out, I put the old one back on. The manufacturer says you need 3-5 bubbles a second and wait 2-4 hours for it to work. Sounds ridiculuous amount of gas for a 6 gallon nano tank.

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