Mystery massacre

[trikeywoman]

Large, mature well planted Freshwater 180l tank with CO2 (Sodastream) system. Running happily for about 10 years with a variety of tetras

Then suddenly........

All the fish started dying. Over the last week all the small fish, cardinal tetras, rummynose, penguin tetras etc have all died off. No sign of sickness beforehand

• Suspected the CO2 straight away and turned it off
• Temperature OK
• Water test is fine, no sign of any problem
• Filter is running well
• Added extra aeration - although fish not showing signs of low oxygen, no gasping at surface
• Did several big water changes - RO water with added nutrients from my own RO filter system
• Wondered whether there was vibration from the existing air stone pump that was disturbing them in some way?

Now the larger fish are looking dodgy. What on earth can it be ?

What's worse is that I am going away for 2 weeks this weekend, I can imagine coming back to an empty tank !

 

[Wills]

Hi welcome to the forum

Have you added anything to the aquarium in the last few weeks/months? If so perhaps it is a disease route to check.

If not and it sounds like its a mature tank so perhaps not, I'd check your electrics, faulty heaters, Co2 solenoid letting too much through. What colour is your Co2 liquid and do you replace it regularly?

Wills

 

[Colin_T]

Need pictures and video of the remaining fish and any dead fish if you took photos of them.
You can upload videos to YouTube, then copy & paste the link here.
If you use a mobile hone to film the fish, hold the phone horizontally (landscape mode) so the footage fills the entire screen and doesn't have black bars on either side.

What is the ammonia, nitrite, nitrate, pH, GH and KH of the water (in numbers)?
What sort of filter is on the tank?
How often and how do you clean the filter?

How often do you do water changes and how much do you change?
Are you adding any plant fertiliser?
Do you do a big water change before adding more fertiliser?

How old is the reverse osmosis unit?
Have you relaced the cartridges in it recently?

Did you have visitors just before this started?
Did you add anything to the tank in the 2 weeks before this started?

 

[trikeywoman]

Need pictures and video of the remaining fish and any dead fish if you took photos of them. I didn't unfortunately (of dead fish) remaining fish behaving normally
You can upload videos to YouTube, then copy & paste the link here. will do
If you use a mobile hone to film the fish, hold the phone horizontally (landscape mode) so the footage fills the entire screen and doesn't have black bars on either side.

What is the ammonia, nitrite, nitrate, pH, GH and KH of the water (in numbers)? Do not have this info but will do so using own kit, LFS confirmed all levels absolutely fine, inc nitrate
What sort of filter is on the tank? Fluval 307 external
How often and how do you clean the filter? about 6 week intervals - see below re water changes

How often do you do water changes and how much do you change? 20% - approx 2 weeks interval
Are you adding any plant fertiliser? No
Do you do a big water change before adding more fertiliser? N/A

How old is the reverse osmosis unit? 3 years
Have you relaced the cartridges in it recently? couple of months ago

Did you have visitors just before this started? ? No
Did you add anything to the tank in the 2 weeks before this started? No - added some small tetras about 1 month ago

 

[trikeywoman]

See answers in your post

 

[trikeywoman]

Should add that the only change in last few weeks was a new CO2 solenoid/regulator. I suspected that right away and disconnected it while doing the water changes and adding extra aeration. But the fish were not showing any signs of gasping at the surface due to too much CO2

I do not have a CO2 monitor. I have been using CO2 for years without a problem.

 

[Colin_T]

How many plants are in the tank and what species do you have

If you aren't adding aquarium plant fertiliser and you don't have really bright light, there is no need or point adding carbon dioxide (CO2). For plants to use supplemental CO2, they need really bright light and lots of fertiliser. If they don't get enough light and fertiliser, they won't use extra CO2 and you are wasting money and adding a potentially poisonous gas that drops the pH.

You also need fast growing plants like Ambulia to make use of CO2. Slow growing plants like Anubias, Cryptocorynes and a few others won't use extra CO2.

 

[jaylach]

Keep in mind that I am not good at all as to diagnostics but the statement of smaller fish dying, and then the larger fish getting 'dodgy', makes me think of the possibility of a parasitic infection.

As has been said, photos/videos would help.

 

[trikeywoman]

Keep in mind that I am not good at all as to diagnostics but the statement of smaller fish dying, and then the larger fish getting 'dodgy', makes me think of the possibility of a parasitic infection.

As has been said, photos/videos would help.

That's a good call. I have since had an expert take a look and he is strongly of the opinion that it is some sort of infection....he thinks bacterial.

Here is a photo of a Siamese Algae Eater - not great but the best I can do

 

[Colin_T]

Need more pictures

The flying fox appears to have excess mucous on it. This is normally caused by something in the water irritating the fish. Big daily water changes and gravel cleaning the substrate can help by diluting anything bad in the water.

Bacterial infections are normally red.

 

[trikeywoman]

Thanks

 

[trikeywoman]

UPDATE. Well I went on holiday for 2 weeks expecting to return to find everything had died. But happily all the surviving fish - mainly the larger ones - seem to be fine.

So I will start cautiously re-stocking with the smaller tetras and monitor the situation closely. Maybe I will never know what caused this

Thanks for all the advice

 

[Ichthys]

If you were using straight tapwater I’d say it’s classic symptoms of “a bad batch” of tapwater. It can happen in the uk. A high level of whatever toxin comes in with one water change and begins to wipe fish out. Maybe there was enough in the tapwater you mixed the RO with… (has there been any roadworks nearby…?) With a lot of toxins different groups / families of fish are affected differently. This could have been a toxin at a level that kills characins but not non-characins… What are the larger fish ?
It’s a good idea to have PolyFilter or at least carbon on hand, although the damage is usually already done. I’d do a few very large water changes before you restock. Totally new water.

You’re changing 20% every two weeks. That’s not much. I would check the nitrates myself, making sure to bang the reagent #2 bottle a few times on a hard surface before you shake it. If the shop doesn’t know you need to do this their test won’t give accurate results.
High nitrates wouldn’t have this sudden effect, but I’d still do my own tests.