Question re O2 vs CO2

[Bellshill Belgians]

Hi,

Hoping for some help from all the people with beautiful planted tanks. I have 3 low tech planted tropical tanks, 2 in amazon style and one SE asian, none have CO2 or ferts added and they grow swords, cabomba, java moss/ferns, indian fern etc pretty satisfactorily. So looking for a new challenge I have a repaired 6 foot tank which I am just installing a 3 d background into. I plan to step up my plant growing on this tank and have invested in a fluval CO2 kit and T5 lights. I will be growing crypts, red pine, hygrophilla and a barclaya.

My question is related to the use of oxygen bubbles. All my other tanks have an air pump running 24/7. Eventually this tank will have some fishy inhabitants. How do I get enough oxygen for the fish while using my CO2 to grow plants? My thoughts so far are to turn the CO2 off at night (coming on again 1hr before lights on). Should I have an air stone on a timer to to come on after the lights go off? Will the plants pearling produce enough O2 during the day? I have had fish gasping at the surface from lack of O2 in years gone by and would like to avoid the experience again.

Hoping for some input as to what others do to balance CO2 vs O2.

Thanks so much

Joanne

[Bilbo]

Based on my own experience only and others will have other (probably better) ideas.

In my larger planted tank I have the CO2 running 1 - 2 bps 24/7. Some people recommend a solenoid to turn the gas off at night and some don't. I don't have one so I cant comment on how good or bad they are. I do know that a DIY CO2 system usually runs round the clock so I leave the bottle running but I never run the CO2 levels high enough to be an issue so I have great plant growth and have never had a fish gasping at the surface.

Sounds like a great tank, best of luck with it.

[phoenix44]

A 6ft tank and a Fluval CO2 kit?

That's a waste of money.

1. It's going to work out too expensive in the long run.

2. Those units are no where near big enough for a 6ft tank.

I'd be returning that if I were you. One of the first questions you must ask your self when you get a CO2 unit is - "how big is my tank?". Those fluval units are only good if used on tanks say 100L or thereabouts. With a 6ft tank, you have flow and length issues to deal with as well.

Apart from that, you do not need bubbles in the tank. Not unless they are CO2 bubbles.

Post some pics so we can actually visualise what the tank looks like.

[kiwiplymouth]

Will the plants pearling produce enough O2 during the day?

Joanne

If your plants are pearling it means that your water is saturated with O2 and that no more will dissolve into it

If you find your fish gasping in the morning it is because your plants are using all the available O2 during the night

To combat this I have an air pump on a timer that turns on when the lights and C02 turn off.

[Zev]

There are two Fluval kits, both for smaller aquariums, Fluval CO2 88g kit, max 151L Aquarium and the Fluval Mini CO2 20g kit, max 57L Aquarium.

The reactor/diffuser for the smaller kit is large and unwieldy and takes up a lot of real estate, especially for anything under a two foot tank.

[Jennifer]

No need to complicate matters. I wouldn't even worry about fish gasping at the surface with a tank that size (as long as it is wide and not abnormally tall ); in my experience, that usually only happens when the water gets very warm or when the tank is highly stocked.

Contrary to myth, it is just fine to have good surface agitation when you use CO2, you may have to add a little bit more CO2 to account for the loss, but it is no problem at all so add an air pump if you like, but I don't think it will be needed. The biggest thing to think about is water flow.

For that size tank, I personally would spend just a bit more and get a bigger CO2 setup (cylinder and regulator), you won't be sorry and it is very affordable to maintain.

[Bellshill Belgians]

Hi,

Thank you all for your comments.

Kiwiplymouth, I was thinking along the lines of what you do with your air pump, but was unsure if anyone would think it was a good idea. At least someone else has had the same idea :lol:

Jennifer, thanks for your input. the tank is 1800mm x 490mm x 450mm so a pretty "normal" shape. In terms of water flow I have a Eheim 2126 to run on it initially, I guess I'll have to see how that does. I have some more old canisters knocking around which can be added in if it doesn't seem enough.

I do appreciate the size discrepancy between an 88g fluval CO2 kit and my tank which is double the size rating, I may have the opportunity to secure another one from a friend who is giving up so 2 would be getting closer to what I am looking for.

So many considerations, so much fun to be had

Thanks

Joanne

[phoenix44]

Contrary to myth, it is just fine to have good surface agitation when you use CO2, you may have to add a little bit more CO2 to account for the loss, but it is no problem at all so add an air pump if you like, but I don't think it will be needed. The biggest thing to think about is water flow.

Please explain.

[Jennifer]

Surface agitation is important for a number of reasons and it will only result in a small loss of dissolved CO2 from the water column.

Depending on the biological system, CO2 can be nearly 100 times more soluble in water than O2 is. For low tech tanks surface agitation is a benefit because atmospheric CO2 helps create a constant CO2 level in the tank. Similarly, when you do a water change, the surface area of the water flowing in a thin stream results in high levels of dissolved CO2, hence why almost everyone will have pearling plants when they do a water change.

Now, considering that O2 is not very soluble, it is easy to see why bubblers do little for dissolving O2, instead, what they do is increase the surface area of the water so that the water is exposed to more atmospheric gas and O2 can dissolve into the water. A duckbill or spray bar aimed at the surface works just as well for increasing turnover of surface water and it doesn't even have to break the surface (although this helps to remove biofilm). One important point, O2 does not displace CO2 in the water column - if the oxygen levels of the water are high, the fish can withstand very high levels of CO2. The challenge is to get high levels of O2 dissolved in the water - pearling plants are great for this and can create a higher level of dissolved O2 than in our immediate atmosphere (however, bigger bubbles that rise to the surface are not dissolving).

In short, get your surface ripple on! It will not only help distribute nutrients to the plants to increase pearling, it will help dissolve more oxygen into the water through surface gas exchange.

[Zev]

I still think for the size tank you have these Fluval units are not economical.

My 2.5kg tank costs around $35 to refill, the Fluval units you are looking at have a specific cylinder that is not refillable and something like $30.00 for 88 grams.

viewtopic.php?f=2&t=49549

[phoenix44]

I don't agree with that Jen, but it's about time we disagreed about something. :lol:

[Jennifer]

Don't take my word for it. Research some aqueous chemistry and have a look about what Tom Barr says. The evidence is out there.

[Warren]

If the correct amount of CO2 is added while the lights are on and the plants are pearling well the O2 content in the water will be saturated and O2 will actually be gassing-off at the surface. With the lights off the plants use O2 and generate CO2. If you're going to control the CO2, I wouldn't turn it back on until the same time as the lights go on as there will already be a good supply of CO2 - no need to turn it on 1 hour before the lights.

Others here have good success leaving the CO2 on 24/7 - I've never tried it but it obviously works. I never tried it because I set up a solenoid on the CO2 from day one and was too chicken to try leaving it on overnight - could have been a costly mistake.

If you are worried about not enough O2 at night you could always turn on airation when the lights are off...

[fordayzbro]

It's a tough one.... I've come close to losing fish to lack of O2 a couple times now.

At the moment I running my Co2 at 2bps and dosing 1.6mls of excel daily and 3.4mls after water changes. The Co2 turns on 2 hours before lights on and 2 hours before lights off. The drop checker is usually yellow when Co2 switches off. To work some O2 back into the tank I just angle my wave maker to the surface and lift my outflow pipe so it's half sticking out of the water when the lights go out and re-adjust in the morning.

I love having healthy plants and an algae free tank but not at the cost of gasing fish to death...... :tears:

[dreams]

I've almost lost fish a few times as well due to lack of O2. Since then I've positioned my spray bars so that they cause surface agitation, but not enough to break the water surface. Haven't had any problems since then

[fordayzbro]

Well it's happened again........

I'm working down in Canty at the moment with my family taking care of the daily tank maintenance. Got a call from my mother today to let me know that some of my fish were gasping at the surface or sunk to the bottom of the tank. I had to talk her through a 50% waterchange, turn off the Co2, adjust the wavemaker and outlet pipe to get some o2 in the water.... The drop checker was yellow at lunch time. I think it was an overdose of excel which has caused the problem.

All the fish are fine now, no casualties. :happy2:

After experiencing this several times now... I think if you want to run pressurised Co2 and dose with liquid carbon, you really need to use a drop checker to keep tabs on Co2 levels.