Help Needed: My Shell Dwellers Are Dying

I’m experiencing a serious issue with my Neolamprologus similis (shell dwellers). They appear lethargic, seem to have problems breathing, have stopped eating, and unfortunately, several have already died—including adults and 2-month-old fry.

Background:

• Tank Setup: The aquarium has been fully cycled for over two years and is set up with aragonite substrate to naturally maintain pH levels. I avoid using chemicals to adjust water parameters.
• Tankmates: They’ve been sharing the tank with barbs for several months without any noticeable conflicts or health issues. The barbs currently show no signs of illness.

Actions Taken So Far:

1. Noticed symptoms and performed a 50% water change.
2. After symptoms persisted for 30 hours, I cleaned the filter and did another 15% water change.

Current Observations:

• Current water parameters: Pictures attached
• I have not observed any visible signs of worms or external parasites.

I’m at a loss as to what’s causing this issue. Any advice or guidance would be greatly appreciated!

How much aeration/ surface turbulence have you got in the tank?

Are you adding carbon dioxide (CO2) to the tank?
Do you add any plant fertiliser to the tank?

What sort of filter is on the aquarium?
How often and how do you normally clean the filter?
How did you clean the filter the other day?

How often do you do water changes and how much do you change?
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 are the numbers of the digital meter for?

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

Contact the water company and find out if they add chlorine or chloramine to the water.

According to the test strips your pH is very low and you have virtually no KH (carbonate hardness) or GH (general hardness). You need to contact your water supply company by phone or website and find out exactly what the GH, KH and pH of your tap water is. If you can't find the info on their website, take a glass of tap water to the local pet shop and have them test it. Write the results down in numbers when they do the test. If they say the water is fine, get the results in numbers.

You also need to find out what the ammonia level is. Test strips don't have ammonia test on it and you need a separate test for that. The pet shop can test the ammonia for you. Get the results in numbers.

The pH for Lake Tanganyikan cichlids should be around 8.5, yours is less than 7.0. The GH for these cichlids should be around 400ppm. If your test strip is correct, the pH, GH and KH are way too low for the cichlids. It is fine for the barbs but very bad for the shell dwellers.

The aragonite isn't doing its job if the pH is 6.4.

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

The pH isn't making them breath heavily, that looks like an infection. At least one fish in the video has a white bottom lip and that can be from fighting or a bacterial infection.

There could also be a lack of oxygen if there's no surface turbulence or you are adding CO2.

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

You need to find out the ammonia level, and get the pH, GH & KH confirmed. You also need to test the tap water for pH, GH & KH.

I would do a big water change and gravel clean the substrate every day for a week or until we figure out what is going on. Lift all the shells up and gravel clean under them. Suck any gunk out of the shells too.
Make sure any new water is free of chlorine/ chloramine before you add it to the tank.

You can leave the plants and gravel clean around them. Have 1-2 inches of undisturbed gravel around the base of the plants (2 inches for the Cryptocorynes).