Oxygen Level Problem - Killing Fish - Please help!

[BarkingCrab]

Hi:

 

I'm running a Minibow 7 FOWLR. Tank has been established since December 2003, cycled without problems. I had a Chromis in the tank soon after it cycled for about six weeks without any issue - he fed properly and seemed fairly happy.

 

About two weeks ago we returned the chromis and introduced a pair of small false percs. Approximately two days after the placement, the larger of the two developed a white puffy growth on the mouth and went downhill from there. Lasted about four days total. The second perc showed no similar symptoms but around day 14 began gasping for air and nosing at the surface. He ultimately expired.

 

I checked all water parameters and the only one that was even remotely out of place was the O2 level, which was way down in the 3-5 mg/l range. I added an airstone and the O2 level shot up overnight to about 7 mg/l, then dropped back down to 5 the next day.

 

I'm completely baffled. Most of the information I've read here and over at Reef Central indicates that having the appropriate water flow at the surface will take care of O2 content, and that airstones are not necessary. I'm running an AC300 and a powerhead in the tank, so movement and surface agitation are not a problem. The tank looks like a bubble storm now that the airstone is in there.

 

I just can't seem to figure out why the O2 has become a problem. What could be affecting it? I do regular water changes, and the inverts (fire shrimp, 4 blue hermits, 2 scarlet hermits, Turbo) are all fine. Any more movement and the tank would be a blender.

 

Suggestions? I realize that at least one of the fish was sick, but the second one seems to have expired due to lack of 02 and I'm very discouraged at this point. I don't want to be killing fish.

 

Other tank specs:

10 lbs LR

10 lbs LS

Stock flourescent lighting

SG 1.023 - 1.024

Temp 76f

 

I'd appreciate any suggestions regarding how to deal with the 02. I've been reading a ton, and can't seem to figure this out.

[theclearblue]

I'd say your two percs died of disease rather than lack of oxygen. It seems like you have more than enough surface agitation. The nosing at the surface is not necessarily indicative of low O2, but is likely a sign of generally poor health.

Now you understand the importance of having a QT tank to be able to treat these diseases outside of the tank.

Could be brook, ich, or any other number of parasites/diseases that seem to be unusually common in clowns right now.

[BarkingCrab]

Thanks for the feedback. I kind of chalked up the perc death to disease, but the O2 issue is still troubling. I've been testing over the past week and the level has not come above 5 mg/l. I'm super careful to follow the test instructions and I've even used two different tests to make sure that's not the issue.

 

No idea how to proceed at this point.

[Korbin]

How high is the O2 supposed to be?

 

The only thing I can think of is maybe you recently added activated carbon just before doing your O2 test? That will suck out 02 if not rinsed first.

 

Heck, maybe you could add some macro algae or something to produce some O2?

[BarkingCrab]

My understanding is that the O2 should be 7mg/l or more. I'm not even close to that point.

 

The carbon guess is a good one, but I don't run anything in the HOB.

 

My brother suggested taking the hood off. I currently leave the hood on 24/7 so as to cut down on the spray and salt creep, but I'm thinking maybe that could be the issue.

 

I'm wondering - do most folks run these small tanks with open tops?

 

-BC

[Korbin]

Most of my tanks weren't open tops.... hhmmm..

 

Maybe you can aim a fan at the water's surface to get some more oxygen action.

[BarkingCrab]

I took the top off last night and re-ran the 02 test this morning. No change. It's still down around 3-5 mg/l. Joy.

[JohnO]

BC,

 

 

Hi there, new here and this is my first post :-)

 

Be careful when measuring O2 and always measure at the same time of day as photosynthesis ceases in the dark and effects O2 levels.

 

John

[Reefmaniac]

Gasping at the top of the tank is usually a sign of parasitic infection of the gills. Could be Gyrodactlyus (hookworms) or Brooklynella hostillis...but to make a diagnosis, I would need more information. Anytime you see those symptoms, you need to get the fish out of the tank and into a hospital setup, treating with copper and formalin...but usually, once you see those symptoms, it is too late. Next time you buy a fish, keep it in a quarantine/hospital tank for 2 to 4 weeks, prophylactically treating with copper and formalin.

[BarkingCrab]

Hi:

 

O2 levels are still low at 3-5. Thanks for the suggestion to measure at the same time of the day, John O. I was doing this as a habit anyway, but the reminder was helpful.

 

I was reading that the tank could become eutropic (sp?) if it's overfed. I'm beginning to think that could be the problem. The clowns didn't eat at all the whole time they were in the tank, and I was out of town for a few days. My wife may have gotten out of hand with the Formula 1...

 

Anyway, the inverts are all fine. The fire shrip acually molted this past weekend. I'm going to do some water changes and see if I can get the level back up.

 

Thanks for all the help here!!!

 

BC

[birdman204]

Originally posted by JohnO

BC,

 

 

Hi there, new here and this is my first post :-)

 

Be careful when measuring O2 and always measure at the same time of day as photosynthesis ceases in the dark and effects O2 levels.

 

John

Wonderful post.

 

Question, is the tank in a bedroom? say where the door is closed often, ambient oxygen content can also affect these levels, as well as PH.

I assume you are doing the test yourself? Taking it to a LFS could affect the amount of dissolved oxygen in the sample.

 

P.S. The reason your chromis may have died is that they are more of an open water planktivore. They need to feed and swim constantly.

[pyrrhus]

chromis didnt die, it was returned. as far as the O2 issue what temperature is the water at? higher temps lead to lower concentrations of O2 same thing with salinity. for instance according to my red sea O2 test at 82.4 degrees F and 1.026 SG the total dissolved oxygen saturation point would be 6.4PPM not sure what the conversion is to mg/l but this may be the issue. as far as correcting the problem try cleaning any filters and gravel in the tank as this could be causing the problem.