Did normal h20 change, then all fish died:(

I have had a 75g fowlr running for about 8 months now. I have a seperate 40g tank were i mix the saltwater before before changes. Last night as i did the 5% change, the fish all woke up and started to swim around up and down the the top and bottom. In the Morning all fish, 2 urchins and fighting counch were dead. All Crabs, snails, and starfish still live. What could have happend?? Something got in the water? I Got a Different Brand of salt mix? i just can't figure it out.

 

did you do anything out of the ordinary? what kind of salt were you using before and what kind are you using now!?

List any parameters..this could help!!

 

Off hand may have you mixed the salt to lean or or rich..?? meaning to little salt in your mix or to much..??

 

thats what I was thinking at first, but if his salinity was off wouldnt the inverts be the first to go? Not sure.

 

He said he only did a 5% change so that is only 3 3/4 gal. of water (not sure why the small amount) and I don't think that is enough to do hardly anything. I am thinking that something got into the spare tank (if not covered) or a bad batch of salt, which is more disturbing to me, as to there is no way to know and all he did was add the new salt and it killed his fish (if it was truly contaminated).
I would have that batch analyzed and if contaminated that company would owe me for the loss of the fish.

 

What type of water did you use? Tap? I found out the hard way with my fresh water tank that my city doses chloramine sometimes and chlorine sometimes. I hadn't added enough dechlor early enough and lost all my neon tetras. The Discus got super pissed at me too.

What makes me suspect this is that you said the fish were swimming up to the surface. I have found with FW fish at least that this indicates a lack of O2. Chlorine and Chloramine can damage gills and you end up with the same result.

Just my 2C so take with a grain of salt, or calcium or whatever.

 

chlorine? did you treat the water?

did you heat it or was it really cold ground water?

 

Params are needed......