Otocinclus inactive / dying

Hi all, any advice would be welcome.

I have a 125liter / 80cm aquarium. Cycled for over 2 months using cycled media from my other tank and beneficial bacteria "Nitrico Goop" when I purchased my first fish.

I have otocinclus that on arrival were busily eating diatoms from all surfaces and looked happy. Very quickly it became apparent that one was very thin and it died within a couple of days. The others have slowly become less active to with another dying. I'm left with 3 that just sit there, on the glass, making zero attempt to find food. However one looks to be doing OK and feeds in one 3rd of the tank mostly. The diatoms are coming back, I have left the glass covered for them also plus i added catapa leaves that have beem sat in another tanks for weeks. Aside from this I have been feeding algae flakes that I was assured they were eating for over 2 months in store and have tried cucumber which one or two seemed to try. I'm so confused as they clearly ate the biofilm and diatoms when I first out them in and one of them still seems OK, why would 3 just sit there and die?

Tank stock is 12 black neons and 15 ember tetra and a few cherry shrimp.

I have lots of filtration with fluval 307, run co2, lights on for 7 hours only. Tank is full of wood and plants to hide in, I'll try to attach a picture.

Not reading any ammonia or nitrite
About 15ppm nitrate
6.6 ph
Kh 6
Gh 11 <is that the issue?
Temp 25 clesius

I hate getting things wrong and really don't understand what I'm doing incorrectly.

I had a recent experience similar to yours. I bought several otos (I think 7) and have 3 that lived. Like you, there was plenty for them to eat. My Ph is 6.7, water clear, healthy fish no ammonia or nitrites, etc.

Otos are usually starving when they get to your tank it seems, and the stress of all of it is just too much for them.

The 3 I have are still doing great, but I had to go through a few to get them to stick around. It was worth it, though! I love them- I call them my 3 Amigos

Yeah, you really have to take a close look at them in the store. If they aren't in top condition at the store, there's a pretty good chance they won't do well when you bring them home. It's possible the ones you bought were just too skinny for even intense feeding to fix. It happens. Otos are wild-caught and throughout their journey through the supply chain, they're kept in clean tanks without biofilms. Suppliers will usually just toss a bunch of algae wafers in with them, but since they're wild-caught, most don't take to the wafers and end up starving.

When you're looking at otos in the store, make sure they have a good head to body ratio and especially look out for a full belly. It should look almost pearl-like, like a little pot belly.

MuddyWaters said:

I had a recent experience similar to yours. I bought several otos (I think 7) and have 3 that lived. Like you, there was plenty for them to eat. My Ph is 6.7, water clear, healthy fish no ammonia or nitrites, etc.

Otos are usually starving when they get to your tank it seems, and the stress of all of it is just too much for them.

The 3 I have are still doing great, but I had to go through a few to get them to stick around. It was worth it, though! I love them- I call them my 3 Amigos
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Can't see myself bothering again if these all die, the 4th one is just stuck there now not looking for food. I wonder if they have parasites preventing them from feeding.