Snail/Invert death, where to start

[Mjp83]

Hi,

I have a 3 yr old RS Reefer 525XL which was thriving up until this summer. I have a large sump with growth light and had massive amounts of Cheato. All was well dosing Kalkwasser.

This August I began to deal with a massive hair algae out break, and at the same time notice the Cheato dying off. I kept to 25% water changes and just scrubbing the rocks, manual removal. As the months went on, I also notice my sand star died, followed by most small snails (turbo snails), followed by my conch, and finally my 3plus year old large Astrea snails. The only thing surviving besides my fish are my fire shrimp and the darn blue legged hermits.
Hair algae now under control using 3 treatments of Flux RX, reduced light and manual removal.

Ok, What are some items to check that may slowly kill off inverts?
1. Water parameters, using RODI to make water
2. Temperature
3. Any rusty Iron near or in water
4. Fresh air supply inlet pipe for tank not in area where exterminator Co can spray pesticides
5. Well water - check if run off enters system, especially when spraying herbicides
6. Larger blue hermits killing off snails for food/housing
7. other predators
8. Get an ICT water test - by whom especially now that we are near a holiday break?

what am I missing?
BTW- 3,4,5 are known issues that happened but not confirmed

Thanks

 

[ISpeakForTheSeas]

what am I missing?

Things I can think of (some of which could be checked by ICP testing) include heavy metal poisoning (like too high of Copper levels could cause) and lack of food.

 

[ナイトコア猫]

Was the nitrate high?