Unexplained Fish Deaths... Help Needed!

[GPHowell]

Basically:
300L Aquarium, heavily planted with LED lighting and CO2, external thermofilter
Tank was cycled for three weeks with 4 ppm NH3 and denitrol
3 Rainbowfish added, water monitored daily for 2 weeks (0 ppm NO2/NO3)
3 more Rainbows added, water monitored daily for 2 weeks (0 ppm NO2/NO3)
Phantom tetra x 20 added and 5 otocinclus + shrimp
water monitored for every two or three days for 2 weeks (0 ppm NO2; nitrate rose to about 10-20ppm then quickly back to zero).

Ten days ago, I found two dead Rainbows in the morning. Six days ago, another two dead Rainbows. Five days ago, 1 dead tetra, yesterday 2 dead Tetra, today another dead tetra...

I've been checking the water frantically for the last few days and it is always (without fail): 0 ppm NO2/NO3; 0.5 to 1.0ppm PO4, 150-175 ppm TDS; pH varies during the day (CO2 addition) from about 6.75 to 7.40 (pH meter).

I've tested Cu (0 ppm) and Fe (0 ppm). I've been doing 20% water changes every few days with RO water (added remin salts to 75-100 ppm TDS). I collect the RO water and let it stand for 24h before adding.

I added an airstone a week ago that runs for 14 hours a day when the lights are off because I was worried about lack of O2 in the water but this hasn't helped...

The fish look healthy (good colour, no visible spots/lesions, feeding well). Occasionally I see one or two fish at mouthing at the surface of the water (this is why I wondered about low O2 levels). The CO2 supply is relatively light (1 bubble/sec) and the drop checker is always blue-tinged, never yellow.

It's starting to get depressing! The plants are all doing brilliantly, as are the shrimp and otos. The rest of the fish all seem healthy but then die and I have absolutely no clue.

I know that I have stocked the aquarium quite quickly but I've been keeping fish for a good 15-20 years and I've always found that as long as the tank is cycled properly and NO2/NO3 levels are closely monitored, this isn't a problem...

I'm also aware that the pH and gH/TDS might be a little low for the Rainbows (although my LFS said it wouldn't be an issue), but this doesn't explain the loss of the tetras...

Wow, this is a long post and I can't think of any more info to add... I've even included a picture. The aquarium is looking really nice but unfortunately the fish aren't enjoying it very much...

Does anyone have any ideas of what to try next because I have no clue?

Thanks

G

 

[dw1305]

Hi all,
I would suspect it is an O2 issue, if you don't have parasites or a stress related disease(FishTB or Camallanus worms would be ones to look for). I might try raising the dKH for a while and see what happens. As as well as needing a lot of O2, the NH3 >NO2>NO3 conversion needs a supply of carbonates. I don't like the quick cycle with ammonia, but in this case if the plants are growing strongly it is irrelevant whether the filter is cycled or not and it isn't a large fish load for 300 litres.

3 Rainbowfish added, water monitored daily for 2 weeks (0 ppm NO2/NO3)
3 more Rainbows added, water monitored daily for 2 weeks (0 ppm NO2/NO3)
Phantom tetra x 20 added and 5 otocinclus + shrimp
water monitored for every two or three days for 2 weeks (0 ppm NO2; nitrate rose to about 10-20ppm then quickly back to zero).

Definitely something wrong with the test kits and/or results, you must have had some NO2 or you wouldn't have any NO3, if you really have no NO3 you can turn the CO2 off, additionally you almost never have no NO3 in a planted tank.

Personally I'd both:
1. Turn the CO2 off
and
2. Throw the test kits away.

cheers Darrel

 

[GPHowell]

thanks for the reply...

I perhaps should have mentioned that when I was adding ammonia (pre-fish) I could observe the oxidation from NH3?NO2?NO3 (test kits) and was using water changes to remove the NO3 that built up. I'm pretty confident that the test kits are fine (Sera). If the plants are growing strongly, wouldn't they consume all of the NO3 that is produced by the (relatively low amounts of) fish waste?

I've just measured the kH and it's about 5° (TDS is about 150); I'll try and increase it slowly over the next few days.

I'll try turning off the CO2 as a short-term solution but what would you recommend long-term?

Is there any way to measure O2 content in water?

Thanks again for the reply, much appreciated!

 

[Brenmuk]

If the fish deaths started to happen after the 3rd addition of fish and shrimp i.e.
- Phantom tetra x 20 added and 5 otocinclus + shrimp
then I would suspect that the fish deaths are ammonia related caused by stocking too soon.

It would be better to add the shrimp then wait a week or 2, then the ottos wait a week or 2, then the 20 tetras split into 2 batches. It isn't simply about numbers either you have to make a judgement based on the size of the fish going in to the tank.

I agree with Darrel chuck away the test kits.

I don't use CO2 but if It were me I would use it in conjunction with additional plant fertilisers such as TPN+ or use the EI method.
How are you feeding your plants?
Healthy growing plants will take up ammonia which should make maturing the tank a lot easier.


What I would do now..
1) I would stop further stocking of the fish for the moment wait until the situation has stabilised and the remaining fish seem settled and there have been no more fish deaths for a few weeks.
2) slowly start adding more fish as above.

 

[GPHowell]

thanks for the reply.

I've tested my test kits this afternoon with some NO2 and NO3 solutions (I work in a chemistry lab) and they're spot-on.

I had been using a JBL daily fert (without N and P) but yesterday I switched to a Tropica fert (with N and P). I've just tested my water again and now it's showing 5-10 ppm NO3 (still no NH3 or NO2) which, I guess, is what you'd expect after switching ferts.

I haven't put any livestock in for about a month and I'll obviously wait for things to settle down before I add anything else.

I'm becoming more convinced that it's an O2 problem...

 

[dw1305]

Hi all,

I would stop further stocking of the fish for the moment wait until the situation has stabilised and the remaining fish seem settled and there have been no more fish deaths for a few weeks.
2) slowly start adding more fish as above.

&

I haven't put any livestock in for about a month and I'll obviously wait for things to settle down before I add anything else.

I'd definitely agree with this.

I've tested my test kits this afternoon with some NO2 and NO3 solutions (I work in a chemistry lab) and they're spot-on.

This is useful to know, if you have a calibration solution it looks like they are real readings. Having said that there is always the proviso that the situation in the tank is a bit different and there may be other anions (like Cl-) that will interfere with the measurement. Do you have access to selective ion selective electrode for NO3/NO2/NH3?

but yesterday I switched to a Tropica fert (with N and P)

This should help your plant growth, the actual demand for P is much lower than for N and K, so it might be worth adding a small amount of KNO3, our sponsors sell this fairly cheaply.

cheers Darrel

 

[GPHowell]

thanks for the reply, Darrel.

Can you get selective electrodes for NO3/NO2/NH3? I didn't think these were available...

And you're right, there is always the possibility that there is something else going on in the tank that is affecting measurements.

For instance, I've noticed that something in my system is increasing the TDS of my water. I use RO water with remin salts (to approx 75-100 ppm) but my tank water always rises to about 160ppm. I think this is some kind of residual inorganics leaching from my substrate (limpopo sand); I've tested this by adding a handful of sand to some RO and monitoring over a few days...

 

[dw1305]

Hi all,

Can you get selective electrodes for NO3/NO2/NH3? I didn't think these were available...

Yes, you can and they work to some degree, but they aren't cheap.

<http://www.nico2000.net/products.htm>
<http://www.nico2000.net/DataSheets/electrodes.html>
<http://www.nico2000.net/analytical/ammonium.htm>

I think this is some kind of residual inorganics leaching from my substrate (limpopo sand); I've tested this by adding a handful of sand to some RO and monitoring over a few days...

I'd expect that it has some calcium carbonate content (shell sand fragments perhaps?), if it isn't you may be able to leach it out with further washing. I think it is meant to be carbonate free, so the result might be quite interesting.

cheers Darrel

 

[GPHowell]

thanks for the info on the probes. Probably too expensive to justify though!