Trochus snails dying while other snails thrive

[Mutton Biryani]

I have a 1 year old 75 gal mixed reef tank that has a variety of inverts including a variety of "snails" (trochus, Mex turbo, nassarius, cerith, strawberry conch, bumblebee, and even limpets)
My trochus (favorite snails) seemed to be the only ones suffering, while the others are doing well. Out of the 10 I had, 2 are dead with empty shell, 6 are belly up, and 1 still attached to glass, but not moving much.

Ive had for them for several months now and they had been active and even growing in size until last week. I noticed that some of them had been turned over and were very lethargic. They just lay there with there soft body hanging out and when I move them it retracts for a bit. I moved them around to rock with good algae and they'd manage to somehow find their way back on the sand upside down.

My parameters are:
Ammonia and Nitrite: 0
Nitrate 5
Phosphate 0.1
Calcium 450
Magnesium 1400
Alkalinity 9


My other snails are thriving. The ceriths seem lay new set of eggs almost every other day. I see some tiny white shells, maybe the baby snails. I have a couple of sea urchins and saw one of them spawning,
For fish I have a pair of clowns, royal gramma, flametip blenny, lawnmower blenny, falco hawkfish, and a cleaner wrasse.
Inverts - Sea serpent star, tuxedo and Halloween urchins, small hermit crabs (blue ad red leg hermits, nothing big), and an emerald crab.

Never saw hermits or hawkfish go after the trochus. To be sure, i isolated the snails with a barrier, and then even moved some down in my second nano tank. No luck still.

I've been puzzled by this issue for a week and I'm hoping to get some your snail advice.

Thanks

 

[ahiggins]

I’ve notice this as well lately. I bought 8 trochus and 15 dwarf trochus. Of those 2 and 10 made it out of delivery. 2 weeks later I have 2 and 8. They seemed to have stabilized now but i also noticed they were less hardy than I remember them (I couldn’t get/find them for the longest time).

 

[Mutton Biryani]

Same here. I couldn't find them for a while at my lfs so they were a late addition. But it's been months and they were stable.

I don't understand how the other inverts are breeding their brains out and the trochus are just dying. I wonder if there is a trochus specific disease they caught. Or if theyre more sensitive to magnesium. I brought this up slowly over 1 week from 1200 to 1350