Lack Of Oxygen?

[Ninja Dave]

Hi,

I'm hoping somebody could help clear this up for me.

I've had my tank set up and added 8 guppies and 6 Salt and Pepper Cory's on Sunday after cycling my tank. They all seemed to be fine when I added them. All feeding and active. Yesterday the Guppies seemed to tend to congregate in one of the top corners. The Cory's weren't very active at all.

This morning two Cory's were dead and one died this afternoon. After looking at the one this afternoon before it died the gills seemed red. After looking into this a bit more it looked like it could have been a lack of Oxygen.

I've tested the water and the Ammonia and Nitrite have remained at 0. The Nitrate was about 80 so I did a 50% water change. I've tested this again and the nitrate is about 30 (tap water is 0). PH is higher than I would like at about 7.6. I'm trying to get this down to around 6.8 which I get from the tap.

The water is quite agitated from the filter (juwel rekord 600 bioflow pump) but I added an air stone this afternoon to try and help things along.

The Guppies seem to have been given new life and their colours have gone from pale to intense colours.

My tank is planted and I ideally do not want the air stone running as its noisy.

Does this sound like a lack of oxygen or something else?
If this is oxygen related, is there a better way of oxygenating the tank other than an air stone so as not to affect the plants (or be noisy)?

Cheers,

Dave

 

[Tizer]

fish can get oxygen from the surface and survive quite happily like that for quite a while. It possibly sounds like a bacterial infection but im not 100% on that because its happened rather quickly. dont worry about the ph in a tropical tank "too" much, keeping it stable is key and generally speaking most fish will adjust. start using products from bottles and you will run into issues. not certain what could have caused the problem but it could have been present when purchasing the fish.

 

[karin]

Sometimes new tanks have an oxygen problem. I keep hearing about it and had one myself. An airstone brought fish that looked near death back to life. (and water stats were spot on) . I have since removed the airstone and there has never been a problem since. If the guppies responded to thei airstone I would go for it for a little bit.

How old is the tank?

 

[backtotropical]

Hi Dave,

Your problem is very very unlikely to be a lack of oxygen. Let me explain that a bit

Oxygen enters the water and carbon dioxide exits the water at the water surface. This is a natural gas exchange and happens all the time, even more so if the surface of the water is agitated, such as by your filter outlet. This is because only a small proportion of your tank water is at the surface at any one time. If the surface is not agitated, then the same small proportion of your tank water will be exchanging gas all the time. If the water surface is agitated, this brings water from below the surface to the surface where gas exchange can take place. This means that over time (depending on how agitated the surface is), all of the water in your tank will be subject to gas exchange, in contrast to an unagitated surface where only a small proportion of the water is ever subject to gas exchange. You can see why agitating the surface does a better job of oxygenating the water.

However that said, (I'm not a science bod, so I'll explain this as best I can) everything strives towards equilibrium (ie. a balance). Therefore, if any oxygen saturated in the water is used by the fish, it must be replaced by something else. This can be anything which the water may absorb, however it will usually be oxygen from the air. Therefore, it is actually very difficult to strip water of it's saturated oxygen content if the water surface is exposed to the air, and it is essentially very difficult to deprive your fish of oxygen even when there is no surface agitation.

I do often hear about problems with oxygen in aquariums, however 9 times out of 10 this will be a mis-diagnosis. The problem is much more likely to be ammonia or nitrite. I know you said you tested for these and they are 0, however your nitrate level has risen from that of your tap water which would nearly always suggest that ammonia has been present.

May I ask how long your tank has been set up? Did you cycle the filter? If so, how did you do it?

I agree that messing with the pH is almost always unwise and unnecessary. All the fish you mention will be absolutely fine in pH 7.6 and trying to change it really isn't required and may do more harm than good.

Regards

BTT

 

[codheadjohn]

However that said, (I'm not a science bod, so I'll explain this as best I can) everything strives towards equilibrium (ie. a balance). Therefore, if any oxygen saturated in the water is used by the fish, it must be replaced by something else. This can be anything which the water may absorb, however it will usually be oxygen from the air. Therefore, it is actually very difficult to strip water of it's saturated oxygen content if the water surface is exposed to the air, and it is essentially very difficult to deprive your fish of oxygen even when there is no surface agitation.

I don't believe that is true. Surely it is much the same as in humans whereby oxygen is 'breathed' in and carbon dioxide comes out. Otherwise the oxygen must disappear for more to be taken in by the water.

Try angling the filter jet out of the water to create as much surface agitation as possible.

I think red gills is a sign of ammonia, I would expect sluggish movement and see them struggling to breathe to be low oxygen

 

[Ninja Dave]

Hi,

Thanks for the replies.

• The filter outlet has always been angled to the surface so there has been reasonable water agitation since setting the tank up.
  
• I did first of all think it was ammonia because of the red gills but as this was 0 I ruled it out (possibly wrongly) and thought it could have been Oxygen levels.
  
• I've had the tank set up for two weeks. It was a second hand tank and the tank was set up pretty much immediately set so the full cycle wasn't needed. I dosed with Ammonia over the two weeks and checked levels daily. It was a bit slow on starting up but within a week it was processing ammonia and nitrite within 12 hours. There was a full week of 0 Ammonia and Nitrite before adding any fish. About 7-8 plants were added on the Saturday and 8 Guppies + 6 Salt and Pepper Cory's added on the Sunday. Thinking about it I've probably overloaded everything too early. Does this seem like a possibility?
  
• With the PH, I'm not adding anything to change it. I dosed the tank with Bicarbonate of Soda when the tank was set up to bring the PH up to 8.0. This has gradually been dropping after water changes as the tap PH is under 7.0. No products are being added to drop the PH.

The fish seem much happier this morning. I don't know whether it's just a coincidence that they seemed happier after the air stone was added or whether it was just from the 50% water change. I'm after Amazon Frogbit to try to tackle the Nitrate levels between weekly water changes. Is a Nitrate level of ~80ppm high as this is what the reading seemed to be at the end of the week before a water change?

Hope this helps.

Cheers,

Dave

 

[Bignose]

However that said, (I'm not a science bod, so I'll explain this as best I can) everything strives towards equilibrium (ie. a balance). Therefore, if any oxygen saturated in the water is used by the fish, it must be replaced by something else. This can be anything which the water may absorb, however it will usually be oxygen from the air. Therefore, it is actually very difficult to strip water of it's saturated oxygen content if the water surface is exposed to the air, and it is essentially very difficult to deprive your fish of oxygen even when there is no surface agitation.

I don't believe that is true. Surely it is much the same as in humans whereby oxygen is 'breathed' in and carbon dioxide comes out. Otherwise the oxygen must disappear for more to be taken in by the water.

BTT is right in that unless you have a very still body of water, or a tank with the head space sealed very tightly, it is almost impossible to have a tank with water that is less than at 100% oxygen equilibrium. When the surface is exposed to air, the water is very quick to absorb oxygen and reach 100% equilibrium with the atmosphere. All the more in a typical fishtank because the filter and fish themselves do a pretty darn good job of mixing the water to ensure equilibrium is reached even faster.

BTT missed just a little bit off in saying "if any oxygen saturated in the water is used by the fish, it must be replaced by something else." The concentrations of oxygen and carbon dioxide in equilibrium with the atmosphere are so low, that they essentially don't see each other in the dissolved water at all. BTT's "something else" is in fact, more oxygen. That is, when the fish use the oxygen, it is a sink, and that sink immediately drives more oxygen from the air into the water to re-achieve equilibrium. In the same way, the carbon dioxide that is excreted is a source in the water, and it is immediately driven out of the tank or consumed by live plants. Nature will always tend towards equilibrium unless additional forces come into play.

I actually think both of you are saying close to the same thing: that with the fish consuming oxygen, there is always oxygen coming into the water.

... or whether it was just from the 50% water change.

It is pretty much never wrong to perform water changes. One situation it would be wrong is if the water hadn't been changed for a very, very long time and the pH was very, very low and there is significant ammonia. The other is if you perform water changes with water with a significantly different hardness. Other than these situations, water changes are pretty much always a good idea, and most fish will respond very positively to them.