How much aeration does a tank require?

So last night I decided to turn off the two air stones I have in my tank in preparation for setting up a CO2 system later this month or next. I've read that air stones will cause the CO2 to off gas before plants can utilize it. I have a SunSun 404b canister with a spray-bar under the water but pointed slightly up so that it moves the surface of the water. I thought that should have been enough to keep the water oxygenated. But after about 3-4 hours without the air stones running, I had two dead Cardinal tetras and all my other fish were gasping at the surface. So I guess I was mistaken on how much oxygen was getting provided by the movement of the water's surface. I turned on the airstones as soon as I saw the issue and everything is doing well this morning.

Can anyone help me out to find the right setup? Is it perhaps the shape/size of my tank (54g corner) that is causing me unexpected results or have I been getting incorrect advice about what is needed to keep enough oxygen in my water for my fish. I'm now really concerned about putting CO2 in the tank without understanding this issue.

 

Don't know about CO2, but this may help.

Aeration
Key to any healthy aquarium is aeration. In an aquarium with even moderate amounts of fish aeration is essential for healthy fish. The aeration not only keeps the fish healthy, it keeps the beneficial bacterial populations healthy. Aeration is one of the five key elements of a good aquarium.

One way to get good aeration is by having the surface of the aquarium be water which has rough turbulent “choppy” appearance to it. This can be the discharge from a filter outlet or the flow from an in-aquarium pump (a “wavemaker” or a “powerhead”). These are so-called “turbulent flow” areas which do an excellent job of aeration. Some prefer to say that the “surface tension” of the water needs to be disturbed in order to get good aeration. This is just another way of saying choppy turbulent flow.

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Wow, OK that article explains exactly what happened. While I had the spray bar pointed up towards the surface, I wouldn't say it was creating "choppy" waves. And it also dispels the impression I was getting on the forums that air stones don't do much. It looks like the air stones I had going were doing the majority of the work here oxygenating the water. Thank you so much for the reference to that article.

I would love to hear back from someone who may be able to advise me on what to do when I get my CO2 setup. Keep the Air stones running? Get a Fluidized bed filter? Get a different outflow for my canister and make sure it is making waves at the surface?

 

I would love to hear back from someone who may be able to advise me on what to do when I get my CO2 setup. Keep the Air stones running? Get a Fluidized bed filter? Get a different outflow for my canister and make sure it is making waves at the surface?

Running CO2 should be done with a moderate to slightly high surface agitation to allow for proper gas exchange. You can have both high dissolved O2 and high dissolved CO2 levels in the same volume of water at the same time.

Ideally:

Run spray bars / filter outputs to they are creating a subtle, yet noticeable ripple across the majority of the water surface.

Run an intake strainer / surface skimmer either on a filter intake or an independent unit such as an Ehiem.

Use more CO2 to help off-set the off-gassing effect of higher surface agitation. CO2 is very cheap, and treat it as if it is free. Trust me, trying to cheap out on running low amounts of CO2 (or off-gassing a lot of CO2 without increasing the amount you are injecting) will create problems, and work against the benefits of owning a CO2 system.

Buy a quality pH probe / pH pen that comes with calibration fluid, calibrate it, and use the pH drop method for determining CO2 levels in the tank:

1) Measure pH prior to the CO2 turning on for the day.
2) Measure pH again 2-3 hours after the CO2 has been on.
3) Subtract the first measurement from the 2nd

You should be around a full 1.0 drop to be at a desirable level of CO2. You can go up to 1.2 / 1.3 but that is walking a fine line. Work up to these levels slowly and make sure you have a decent amount of surface agitation to allow lots of O2 to go with lots of CO2.

I hope this helps.

 

I've used the skimmer attachment on my intake before but stopped using it because it was causing some air to get into the filter and blowing bubbles out of the outflow and I though that was bad for the impeller on the canister. Now I'm thinking that may have been the way it was supposed to work. I have some duckweed in that tank because my Moonlight Gourami likes to eat it and that may not be good with a surface skimmer. So maybe I will just keep my airstones going and go from there.

I've been looking at the pH drop method but I was concerned about being able to determine my exact starting pH because it seems to be right at the top of the low pH range and the bottom of the high pH range when I use the API test kit. Do you have a meter you would recommend?

 

I've used the skimmer attachment on my intake before but stopped using it because it was causing some air to get into the filter and blowing bubbles out of the outflow and I though that was bad for the impeller on the canister. Now I'm thinking that may have been the way it was supposed to work. I have some duckweed in that tank because my Moonlight Gourami likes to eat it and that may not be good with a surface skimmer. So maybe I will just keep my airstones going and go from there.

I've been looking at the pH drop method but I was concerned about being able to determine my exact starting pH because it seems to be right at the top of the low pH range and the bottom of the high pH range when I use the API test kit. Do you have a meter you would recommend?

Do not run an airstone in conjunction with CO2, that would cause too much off-gassing and inconsistent CO2 levels, which in my opinion is worse than no CO2 at all.

$20 pH pen from amazon is accurate enough for our needs, unless you want to run a full-out pH controller such as an American Marine Pinpoint pH controller.

Controller is the top of the line option for running a CO2 system, pH drop is the same principle, but it involved more direct labor and you are adjusting CO2 rates instead of the controller.

What size tank are we talking here? Flow meter might be needed depending on the rate of CO2 used.

Dwyer RMA-151-SSV is a good option.

And no, the surface skimmer should be adjusted so there is a slight skimming action, resulting in no bubbles making their way into the filter, that is not the way they are designed to work.

 

My tank is the one listed in my profile, 54g corner tank. Profile is up to date on configuration and stocking.

If I don't run air stones, then I need to figure out the best way to get surface agitation going on that still oxygenates my water. I guess I will need to play around with some different configurations on my outflow and watch closely on how my fish act. Or maybe I should add a powerhead or a moving bed filter. Would either of those cause too much off gassing for CO2? My concern is that since my tank is not a standard rectangle, if I configure the outflow for more surface agitation then I will not get good flow and detritus will build up in some spots. Currently I have the flow configured from the back corner pointing up and towards the font of the glass. Then I have my intake in the back corner just above the substrate. This seems to work really well for keeping detritus from building up.

Once I find a good configuration without CO2, will adding CO2 affect that? Since adding CO2 doesn't affect how much Oxygen is in the water?

The surface skimmer that came with my filter doesn't seem to have an adjustment. It just floats to the surface, and ends up sucking in air. Maybe I am using it wrong, I will look up the manual.

 

So last night I decided to turn off the two air stones I have in my tank in preparation for setting up a CO2 system later this month or next. I've read that air stones will cause the CO2 to off gas before plants can utilize it. I have a SunSun 404b canister with a spray-bar under the water but pointed slightly up so that it moves the surface of the water. I thought that should have been enough to keep the water oxygenated. But after about 3-4 hours without the air stones running, I had two dead Cardinal tetras and all my other fish were gasping at the surface. So I guess I was mistaken on how much oxygen was getting provided by the movement of the water's surface. I turned on the airstones as soon as I saw the issue and everything is doing well this morning.

Can anyone help me out to find the right setup? Is it perhaps the shape/size of my tank (54g corner) that is causing me unexpected results or have I been getting incorrect advice about what is needed to keep enough oxygen in my water for my fish. I'm now really concerned about putting CO2 in the tank without understanding this issue.

I don’t know if anyone mentioned this already, but you could put your air pump on a timer so that it kicks on at night (when plants are growing and not releasing oxygen) and then the CO2 comes on during the day when plants would be using it.