Kuhli loach dying

[Elephant nose 4]

Hi over the past 2 days my kuhli loach have been dying. No signs, just swimming erratically then they're gone.
I'm devastated i don't know what I've done wrong.
Had them 3mth they look healthy.
Tank 29 gallon
Ammonia 0
Nitrite 0
Nitrate 10
Ph 7
Change them on Saturday, but I've just done another Change since there's been deaths and incase I'm missing something.
Any help would be appreciated

 

[MaloK]

The fist thing to make sure when fish start to swim erratically is that the tank is properly oxygenated. And even so I add some more.

Verify if the filter performs as supposed to.

If the fishes are used to regular water changes I immediately perform a very large water change 80%-90%. If not, I automatically add a large amount of activated carbon to the filtration system and start an intensive as big as possible water change schedule trying not to swing parameters too fast.

Verify That the heaters are working correctly and at good temp.

Contaminant could have entered the tank. Anything out of the ordinary lately, kids around?

I wouldn't think of illness or anything else given the categorical suddenness how it happened.

My first line of thought would be contaminant.

 

[Elephant nose 4]

The only thing different I've done is added Catappa leaf and mineral block to my tank
I've done a 70% water change , oxygen levels are good , 2 filters are running.
Heater is good
Other bottom dwellers gobies and red Lizard also shrimp are ok
Totally stumped
Thank you

 

[MaloK]

Some anecdotal reports suggest Kuhli loaches can experience neurological problems or "whirling disease" from pathogens, causing erratic swimming and sudden death. Many mentioned a nutritional deficiency could be promoting the phenomena.

Shrimps are a very good canary and would be the first to be afflicted habitually.

What is the substrate in your tank ?

 

[Elephant nose 4]

It's sand, tank has been up and running for 12 years

 

[MaloK]

From your pictures I was pretty sure you where experienced.

Besides something that could have developed or entered in the substrate, I have no idea what could happened.

 

[Elephant nose 4]

Yes i am kept fish for 30 year's just haven't a clue what's happening? Just going to carry on with pwc tomorrow and hopefully I won't lose anymore

 

[Elephant nose 4]

I've also never kept kuhli loach before