Fish dying, not sure why

[Stevetheadi]

I have a small (64L) tank that with corydoras (two), harlequin rasboras (two) cherry barbs (four). There were a few more but sadly I have lost 5 fish over the last couple of days.

Any suggestions would be appreciated.

I've done a 70% water change today. The remaining fish are still listless, look poorly.

Tank size: 64L
tank age: three years, planted, inert substrate
pH: 8.5
ammonia: nil
nitrite: nil
nitrate: unsure of the number but relatively high, it's how it comes out of the tap.
Hardness: high
413.715 mg/l (or parts per million)

23.499 °dH

tank temp: 27C

Hardness and pH have been high since the tank was established three years ago so I doubt that's a factor.

Fish Symptoms (include full description including lesion, color, location, fish behavior): fish start off by being listless, hovering by the bottom of the tank then they soon die. No visible injuries or discolouration. All the fins intact and normal.

Volume and Frequency of water changes: Every week, 30%

Chemical Additives or Media in your tank: TNC light

Tank inhabitants: see above

Recent additions to your tank (living or decoration): some wood bought from a good fish shop, now removed. A few floating plants.

Exposure to chemicals: only TNC

 

[Colin_T]

Need pictures and video of the fish, and a picture showing the entire tank.
Upload videos to YouTube, then copy & paste the link here.
If you use a mobile phone 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 end.

What is TNC and what does it contain?

What sort of filter is in the tank?
What filter materials/ media are in the filter?
How often and how do you clean the filter?

Do you gravel clean the substrate when you do a water change?
Do you dechlorinate the new water before adding it to the aquarium?

What did you do to the tank a couple of days ago just before this started?
Did you have any visitors around that time?

Have you changed buckets, hoses or anything else around the time this started?

Did you wash/ soak the new wood before adding it?
When did you add the wood and when did the fish start dying?

 

[Stevetheadi]

Here's a video:

I can't take photos of individual fish but you can see a couple on the video.

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What is TNC and what does it contain? - TNC lite is Nitrate and Phosphate free. It is specifically designed for use in lightly planted aquariums or for aquariums where a higher fish population provides the necessary Nitrate and Phosphate. TNC lite contains Potassium, Magnesium and Trace elements

What sort of filter is in the tank? Interpet CF2
What filter materials/ media are in the filter? - bio and filter pads
How often and how do you clean the filter? - monthly, replace filter pads

Do you gravel clean the substrate when you do a water change? - on the surface only
Do you dechlorinate the new water before adding it to the aquarium? - yes

What did you do to the tank a couple of days ago just before this started? - added wood
Did you have any visitors around that time? - no

Have you changed buckets, hoses or anything else around the time this started? - no

Did you wash/ soak the new wood before adding it? - I washed it in boiling water
When did you add the wood and when did the fish start dying? - two days ago. Fish started dying one day ago.

 

[Colin_T]

You probably don't need the TNC fertiliser if you have hard water that contains magnesium. Your water company's website should have a water analysis report that will tell you exactly what is in the water. If you don't understand the report, post a copy on here and we can go through it for you.

Potassium is used by terrestrial plants to produce fruit and flowers, it does virtually nothing for most aquatic plants.

The trace elements are probably ok to use. Depending on what is in your tap water, you might be better off just using a fertiliser with trace elements.

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It's preferable not to replace filter media unless it starts to fall apart.

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If the fish started dying the day after you added the wood and nothing else has changed, and the fish aren't showing any external signs of disease (like in the video), they were probably poisoned by something on or in the wood.

I would do a 75-90% water change and complete gravel clean each day for a week and see if it helps.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.

If it is poisoning they should improve after one or two big water changes.

 

[Stevetheadi]

You probably don't need the TNC fertiliser if you have hard water that contains magnesium. Your water company's website should have a water analysis report that will tell you exactly what is in the water. If you don't understand the report, post a copy on here and we can go through it for you.

Potassium is used by terrestrial plants to produce fruit and flowers, it does virtually nothing for most aquatic plants.

The trace elements are probably ok to use. Depending on what is in your tap water, you might be better off just using a fertiliser with trace elements.

-------------------

It's preferable not to replace filter media unless it starts to fall apart.

-------------------

If the fish started dying the day after you added the wood and nothing else has changed, and the fish aren't showing any external signs of disease (like in the video), they were probably poisoned by something on or in the wood.

I would do a 75-90% water change and complete gravel clean each day for a week and see if it helps.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.

If it is poisoning they should improve after one or two big water changes.

Thank you.

I'll do as you suggest.

I use Seachem Prime to dechlorinate, maybe I'll use a bit extra.

 

[Stevetheadi]

The water in my area is very hard.

	401.283 mg/l (or parts per million)	:Calcium Carbonate
	160.513 mg/l (or parts per million)	:Calcium
	27.929 °C	egrees Clark
	40.128 °F	egrees French
	22.793 °dH	egrees German
	4.013 mmol/l	:Millimoles

 

[Stevetheadi]

the full water quality report - it's very long!

 

[Essjay]

This is what TNC Lite contains
1% K, 0.4% Mg, 0.08% Fe, 0.018% Mn, 0.002% Cu, 0.01% B, 0.01% Zn, 0.001% Mo, EDTA.

 

[Stevetheadi]

This is what TNC Lite contains
1% K, 0.4% Mg, 0.08% Fe, 0.018% Mn, 0.002% Cu, 0.01% B, 0.01% Zn, 0.001% Mo, EDTA.

It's good stuff. Feeds plants in an inert substrate. Made a big difference to mine.