Bizarre snail death problem in second hand tank

Ok, so I have a problem with one of my tanks that I just can't work out the cause of. I have 4 other tanks and have been keeping fish for 10 years but have never had an issue like this.

Background: A few months ago I got a secondhand fully set up tank off FB marketplace, along with some (surprise) fish with tumours and lots of equipment. The tap water in my area has a TDS of around 30 and the seller lived closeby and should have the same water supply, but when I got the tank home and tested it the TDS of the water in the tank was somehow at 793. I have no idea what the TDS was composed of as the water didn’t have much gh or kh and the nitrates were 30ppm (no ammonia or nitrite), so that leaves a lot of ppm a mystery.

I’ve been doing a lot of water changes to bring it down to a more appropriate level for the fish in there, it is now at 200. But I have a strange problem.

While the parameters on tests look normal, and fish seem perfectly healthy (apart from the ones that came with the tank that already had tumours, they still have those), any snail I try to add dies within a day. Even MTS, which I thought were pretty indestructible. (I used the same acclimation process for the snails added to this tank as snails I added to another tank at the same time and didn’t lose any of the ones in the other tank). I’ve tried running carbon and also cuprisorb (thinking it might be copper residue) but it still happened after a few weeks of those in the filter. The strangest thing is that cherry shrimp are completely fine. Only snails die. But I'm not sure what could be killing snails but not shrimp.

Looking through the equipment the guy gave me (which was all his aquarium equipment) there are some ph adjustment products, aquarium salt, fertiliser and an algaecide with appears to just be glutaraldehyde. When I picked the tank up he did say he had trouble getting the ph 'right'. So I'm guessing he used a lot of products. I don't use any of those products so I have no experience of whether they could kill if overdosed.

I can only assume he used a heap of one of those at some point and it’s killing the snails. Does anyone have any idea what could be in there that kills snails but not shrimp, or how to remove it? I might just give up on putting any snails in there but I really want to work out what is causing it.

 

Just because the snails are dying dosnt mean the shrimp should, in cases where there's high ammonia or nitrites then yes it would kill both
Meds like Fenbendazole, Planaria zero, No Planaria are shrimp safe yet will kill your snails
It seems to me and I'm not sure what it is that something you have is doing exactly that
This is the only conclusion I can think of but dosnt solve the issue

 

True. I guess I thought the shrimp would also be dying because at first I thought it might be residue from algaecide with copper in it. But it doesn't look like it is copper, after all.

It's possible the original owner used meds in the few months he had the tank but they weren't in the equipment he gave me. I would message and ask him, but it was a fair while ago now and that might be weird. I thought carbon would remove any meds but there could still be residue on the substrate and everything. Maybe I'll leave it another few months and keep doing water changes then eventually try another Malaysian Trumpet Snail to test it.

When I first got the tank, something in the water was also causing a lot of the plants to melt, but, unlike the snail thing, that resolved after water changes over a few weeks.

 

I thought the same thing that the previous owner used something
We had another member with exactly the same problem with snails dying but it was one of her tanks and even after water changes and a few months later she tried again and they still died,
I don't think she ever got to to problem

 

I thought the same thing that the previous owner used something
We had another member with exactly the same problem with snails dying but it was one of her tanks and even after water changes and a few months later she tried again and they still died,
I don't think she ever got to to problem

Yesterday I tried to add a snail to a seperate tank I set up recently (with cycled media and good parameters) and the same thing happened. The only similarity I can see between the two tanks is that I used the same black silica sand to cap the substrate. I've never used it in any other tank, and in every other tank the snails are fine.

I also had a search for other instances of people having this problem and a couple mentioned silica sand too. Do you think it could be related? Like this particular sand could be acting kind of like dichotomous earth and killing the snails by slicing them?

Maybe I should try capping the substrate with something else and see if it helps?

 

It sounds like it's gonna be a process of elimination