Invertebrate death mystery

[Ian_B]

A couple weeks ago most of my snails and my one emerald crab died. There was one remaining small cerith still cruising around and two turbo snails that have just been staying in one place, not moving much. The two clownfish are fine and the euphyllia corals and zoas good. There is some algae growing in the tank, film on the glass, a little hair algae and some bubble algae I’ve been trying to remove but nothing crazy.
I did some tests and found:
Nitrates - 10ppm Phosphates - 0.02ppm calcium 415 magnesium ~ 1250 dKH - 10 (which is a little high I think because I use aqua forest which should be 7-8) salinity - 1.026 sg
I did a couple water changes over two weeks and got some more trochus and cerith snails and another emerald crab. By the next day they were all either dead or laying on their side/back not moving. I brought my water in to my lfs to test for copper and it came up with nothing. They tested for ammonia also and came up with nothing. I ordered an icp water test to see if that comes up with anything, but in the meantime I wanted to see if anyone had any ideas. I’ve been running carbon and checked my magnet to see if it was corroding at all, but it looked fine.

 

[The_Paradox]

Tank running warmer than normal? Confident in the salinity reading?

 

[Ian_B]

Normal temp, 76. I calibrated my refractometer to make sure the salinity was good.

 

[Ian_B]

Is there something inverts might be more sensitive too than fish or lps corals?

 

[The_Paradox]

Is there something inverts might be more sensitive too than fish or lps corals?

Magnesium and nitrate. What you described I assumed was sudden though.

 

[taricha]

Grazers can be sensitive to toxic algae. Does any of your algae look like dinos?
toxicity shows up as dad of snails and some snails that live become sluggish and stop moving.

 

[Ian_B]

No, I haven’t noticed anything that looks like dinos. I checked algae from a few spots with a loupe and no dinos. I do have two nassarius snails that seem to be doing fine. They’re out cruising now after feeding the fish, so toxic algae is an idea. Anything besides dinos that they might be toxic to?

 

[taricha]

Anything besides dinos that they might be toxic to?

Other toxic algae killing CUC are much less likely.

If stuff acts like there may be toxins, but chem tests and ICP shows nothing, I'd run small amounts of GAC and change it frequently and do more water changes - in case of some organic toxin presence.