fast death of two clowns

[asalot]

Hello
I have a big trouble, today 2 of my clowns are died, I ask you to help me determine the reason

Aquarium: 40l (10gal)
a lot of dry big stones (my son’s wish, this is his aquarium)
air pump
filtration: tetra whisper 10 (filter: sponge, ceramic rings, coal)
pump for flow
heater
sand like soil

2 blue crab: one big
1 turbo snail
1 Peppermint shrimp
2 dead clowns
1polyp zoas
1 green star polyps (I doubt, because the branches are not green)
1 duncan coral (I was looking in the internet myself, my opinion)

Aquarium start was 5 months ago
I bought fishes 1 month ago.
zoas, corals, shrimp, snail were bought a week ago

Let's start from yesterday
water parameters for yesterday:
Ammonia, nitrite-0
nitrate - 0-5ppm (I doubt, rather, 0, because the water is dark yellow)
ph 8
kh 11 dkh
salinity 1022
calcium 420
temperature 78
magnesium - I do not know (the test has not arrived yet)
phosphate - I do not know (the same reason)


Yesterday morning, GPS (green polyp) closed over 40 minutes and no longer opens (2 days already), a zoas is half closed, the fishes all the time sat under the stones and didn't climb out, refused to eat

I checked the water and saw that the salt was low, tried to level it, poured about 1g of water into the aquarium in a little salty (maybe it was not necessary to do so)

In the evening I was worried about the fishes, I began to examine them, but they were sitting in the hole under rocks, it was hard to see them. I saw like a little white bloom, also deep breathing, and a little torn tail.

I read on the forums that maybe this is a Brooklynella or fluks. I made a freshwater dip for 3 minutes, then I ran them back, they behaved calmly, I calmed down, I think there is time to buy medicine, and then this morning

Approximately 1 hour, they are died.

symptoms: heavy breathing, loss of appetite, loss of orientation, could not swim normally, finally felt to the bottom on the side and that was all.

Water parameters are identical to yesterday.

I put the video and photos in one folder (they are not inserted here)

https://drive.google.com/open?id=1XP8EWuT82SAfxqb6F8O13dlI3THfVCCD


Please help me understand what I did wrong.

there is an orange hedgehog on one of the photos and next to it there is such an awkward curved stick, it's like my green star polyps (img 0853)

 

[Maritimer]

Hello, Asalot - Welcome to Reef2Reef, though I'm sorry that your first post is a sad one!

Can you tell us how you went about raising the salinity of your water? Fish can often tolerate salinity falling moderately quickly, but rising salinity can be a greater problem. The best way I've found to raise salinity is to use saltwater as top-off, rather than freshwater. That way, the salinity rises very gradually, over days or even weeks.

It's possible that some of our disease experts, @Humblefish, @Big G or @HotRocks could offer insights that I'm missing.

~Bruce

 

[asalot]

It was quick. I put the additional water to my tank

 

[Maritimer]

It occurs to me that it's also possible that some kind of contaminant got into your tank somehow ... anything you can think of?

~Bruce