Snails died

[welshgazz]

Hi all so my tank is roughly 2 months up and running, I bought it from someone who had it running until I collected it so all the rock was wet and upon setup in my house it took no time to re-establish. I have a healthy aquarium with 6 fish some very small hermit crabs a cleaner shrimp and some trochus and nassarius snails. The issue is that I added 3 turbo snails for algae control and they moved about for about 2 weeks then they all died. My rocks are all green and there is green hair algae present so I'm puzzled why they died. Is there not enough algae? My fish are nothing predatory:
Pair percula clowns
Royal gramma
Chalk bass
Bengai cardinal
Chalk goby

Parameters are:
Salinity 1.025
Nitrate 5.0
Phosphate 0.25

Photo attached with lights white to show what tank looks like. The lights aren't that white or bright normally.

 

[Euphyllia97]

Can you ask the previous owner if he ever used copper to treat any disease in the tank?

 

[Gumbies R Us]

Where are you getting the snails from? LFS by me had a tendency to sell me snails that wouldn't last long. Some would last almost a year while others would last maybe a week