Dissolved oxygen levels

[Matty24]

Does anyone measure dissolved oxygen levels in their aquarium.. ive recently lost 2 amano shrimp and a molly I'm pretty sure the molly had been in a fight with another, fins had been attacked overnight I separated him after seeing something had happened and he wasn't feeding with the others.. but the shrimp I have no idea other than they were only added about 2 weeks ago and my otos seem to be laying on the bottom more over the last couple of days I'm wondering weather the temp is having an effect my heater is set at 26 degrees normally but ive dropped it to 24, no fish gasping on the surface but after reading a little on the Internet I keep coming across fish laying on the bottom is also a sign of not enough oxygen maybe im worrying abit to much but when you have that feeling something isn't right kind of makes you think.. I done a 50% water change as I do every Sunday, I've also done a water test and ammonia, nitrate and nirite is all 0 hopefully I'm worried for no reason and will keep my eye on things

 

[connorlindeman]

Does anyone measure dissolved oxygen levels in their aquarium.. ive recently lost 2 amano shrimp and a molly I'm pretty sure the molly had been in a fight with another, fins had been attacked overnight I separated him after seeing something had happened and he wasn't feeding with the others.. but the shrimp I have no idea other than they were only added about 2 weeks ago and my otos seem to be laying on the bottom more over the last couple of days I'm wondering weather the temp is having an effect my heater is set at 26 degrees normally but ive dropped it to 24, no fish gasping on the surface but after reading a little on the Internet I keep coming across fish laying on the bottom is also a sign of not enough oxygen maybe im worrying abit to much but when you have that feeling something isn't right kind of makes you think.. I done a 50% water change as I do every Sunday, I've also done a water test and ammonia, nitrate and nirite is all 0 hopefully I'm worried for no reason and will keep my eye on things

Pictures or better yet a video of the fish? If it were a lack of oxygen then there should be improvement after a water change.

 

[Naughts]

It's not clear how long the tank has been running and we could do with more background information, but if you suspect oxygen is an issue there is no harm in increasing it. Point the filter outlet so that there is disturbance on the surface and add an airstone or two.

 

[Byron]

Insufficient/low oxygen is unlikely the issue. The first sign would be increased rate of respiration of all fish, then remaining at the surface and gasping for air. Of course, these symptoms are present for many things, but the point here is that you are not seeing them (I assume) so it is not that.

In addition to the photos/video if possible, knowing water parameters (GH and pH especially), and results of tests for ammonia, nitrite,, nitrate can be helpful. I doubt it is ammonia or nitrite, for same reason as my sentence above, but nitrates are possible. There is no harm in ensuring good surface disturbance as the member above mentioned.

 

[Colin_T]

If there is a reasonable/ moderate amount of aeration/ surface turbulence, you should have pretty high oxygen levels in the water. And as @Byron mentioned, if it was oxygen starvation (low levels), all the fish would show the same symptoms and be up near the filter outlet or by the surface.

Poor water quality (ammonia, nitrite, high nitrate), chemicals or pollutants that have gotten into the water will also cause fish to gasp. If only one fish is gasping it might have gill problems (flukes, fungus, bacteria), or the fish could be in pain. Fish like oxygen rich water when in pain and they will often hang out near the surface or a filter outlet.

If a fish suddenly stops eating and sits at the surface gasping, it could have an internal bacterial infection or internal organ damage/ failure possibly caused by a disease or just poor genetics.

What does the fish's poop look like?
Is the fish eating anything?

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A water temperature of 26C is unlikely to have a low oxygen level with some aeration. If the water temperature is 28-32C, then the oxygen levels start to drop. If the water does get this warm, get another air pump and have an airstone bubbling away in the tank to maximise the oxygen levels.

 

[Matty24]

Tank is 130lt (32 us gallons) Tanks around 3 and a half months out I'm using a fluval u3 filter, medium size sponge filter, as of yesterdays water test 0 ammonia, nitrite and nitrate, gh is 16, kh is 12, I have 11 platys, 12 otocinclus catfish, 3 shrimp, fairly well planted with co2 injection and el dosed with seachum products will attach a photo of the tank its all maintained on time dont miss water changes, as for otocinclus fish laying on the bottom they seem chilled out no rapid Gill moment just seemed strange this morning I have flicked the light on and they are all stuck to the glass they all seem happy this morning little round bellys, the platys are the same as every begging for food

 

[Colin_T]

Is the CO2 running continuously 24/7?

If the CO2 is run at night when the lights are off, the plants won't use it and it can build up to toxic levels. This is more likely to occur in heavily planted tanks with little to no surface movement.

CO2 units should be turned off an hour before the lights go out and come on when the lights come on. Alternatively have an air pump come on when the lights go out so you get rid of excess CO2 and keep the oxygen levels high.

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High levels of CO2 can cause the pH to drop and this could adversely affect common livebearers like mollies, guppies, swordtails and platies. All of whom do best in water with a pH above 7.0 and a GH around or above 200ppm (250ppm for mollies).

If there is insufficient carbonate hardness (KH) in the water, the CO2 can cause a rapid and sudden drop in pH that could kill fish that don't like acid water.

Shrimp will also be affected by sudden drops in pH.

 

[Matty24]

my co2 comes on 3 hours before my lights come on and goes off an hour before lights go off my ph is generally around 7.0 > as I say the platys/mollies don't show any signs what so ever they are always happy as Larry, just that slight change in the otos worried me, this morning they looked fine maybe reading whats on the Internet isnt always the best.. which is why I come on here for more actual knowledge from people who know best

 

[Colin_T]

I wouldn't have the CO2 come on 3 hours before the lights do. If you want the CO2 on before the lights, have it on 1 hour before lights on.

You can also monitor the CO2 in the tank water before lights come on. Do it a few hours before and every hour or half hour until the lights come on. You might not need to have the CO2 on 3 hours before and enough might build up in 1 or 2 hours. This would reduce the amount of CO2 you use and save money.

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Without seeing the molly, it is impossible to say what killed it, but I doubt it was lack of oxygen, especially considering the other fishes are fine.

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Are you testing for other fertiliser nutrients before doing a water change or adding more nutrients?

Sometimes the plants don't use all the nutrients and when you add more fertiliser, the levels can build up. It happens slowly but can get to a point where it affects the fish and weakens or kills them. Doing a bigger water change before adding more fertiliser would help reduce any leftover traces that haven't been used.

I don't think this would be a problem in your tank due to the number of plants, but it might be worth checking every now and then.

 

[Matty24]

I believe the molly that died due to another fish attacking it possibly the other male in the tank looked like 1 of his anal fins had been attacked looked as if he could or use 1 side of his body anal fin was sticking out to the side, was more worried about the otos more than anything I following a dosing schedule, I have had to adjust the iron in which I put it in as later into the week it seemed it was causing a bacterial bloom but I was dosing double the iron at the time to try and give my rotala a boost as growth seemed really slow, so the iron levels are adjusted to sort the plants, but always on a Sunday its a rest day no ferts go in and I do a 50% water change to reset the tank for the following week it seems to work really well everything is growing nicely, during the water change of course i treat the water and try to keep the temp as close to the temp on the tank to try not cause any stress I believe the co2 comes on 3 hours before I could be wrong and it might be 2 hours I will have to check the timer when I'm home but certainly goes off an hour before lights go out

 

[TwoTankAmin]

Colin is right on when to turn the CO2 on and off. I used to run mine 24/7 without issues but i ran a somewhat lean mix. 1 bpm in a 50 gal which likely held about 25 gals of water.

Given the mass of plants in your tank, the one thing that is not lacking is oxygen.

 

[Matty24]

This is the sort of thing I'm talking about couple of otos on the bottom look perfectly fine no rapid breathing or anything the others are dotted around on the glass or on the val maybe im thinking into it to much but I never remember them laying on the bottom is that normal behaviour maybe its something to do with the light as they are laying under the filter there where its most shaded I spose each oto could be slightly different like us?

the co2 was coming on at 10am and lights come on at 12am, co2 goes off at 9pm and lights go off at 10pm I checked my timers when I got home as i couldnt 100% remember

 

[Stan510]

ADA makes a machine that adds pure oxygen to the aquarium. All I can say for sure is, my tank water became clearer when I added an air pump into the vortex of a power head. More aeration= better more efficient bacteria in the filter.

 

[Essjay]

A water temperature of 26C is unlikely to have a low oxygen level with some aeration. If the water temperature is 28-32C, then the oxygen levels start to drop. If the water does get this warm, get another air pump and have an airstone bubbling away in the tank to maximise the oxygen levels.

The water temperature may be above 26 deg C as we have a heatwave at the moment. It's the heater that was set to 26 deg not the actual water temp. And where Matty24 lives is in the amber alert area for the weekend - Norfolk shouldn't see the 35 deg predicted for the south east but it could still reach 30+ deg.

 

[Matty24]

I cleaned my filter out tonight I was absolutely stock at how dirty the media was, the filter must of been only working at half power I actually have so much more flow again now.. the otos are acting how they used to shoaling and racing about the tank, I'm sure that filter has only been in the tank month and a half how often should the media be rinsed? (It was cleaned in tank water ) also I had a little problem with a bacterial bloom over the last couple of weeks would a dirty filter have a contribution in the bloom?

Yes like @Essjay said where i live we are having above average temp at the min talks of 40c in london by the end of the week where i live i cant imagine it will be as much as 40 but we will have low 30s for sure by the end of the week yes my heater will only kick in if the water temp drops below whatever its set at ive dropped it to 24 for the time being as it is really humid at the moment