a fish dies every day help

this is a shot in the dark, but what was the tank being used for before you got it? I got a filter off a friend who used it on a baby gator tank. After a thorough cleaning, it killed my Dempseys...
 
I can't honeslty thing of anything that would go in a SW tank that would remain in high enough concentrations to be lethal, even without a thorough rinsing. Even heavy salt encrustations wouldn't be lethal--at that volume, the salinity wouldn't even 1% without adding 17-18 pounds of salt.
 
When all is said and done, looks like roof runoff or collection barrel to be most likely source of contamination. Nothing else seems to add up.
 
tank was salt water withsump , we took sump off and I added a canster filter , 3 more fish sick today

There's no live rock or sand leftover from the old saltwater setup, is there? The only other thing I could think of would be a big ammonia spike from any of the remaining sw critters dying and decomposing that went undetected and has now stabilized, but the fish were still damaged?

I'd still recommend redoing the collection. That seems to be the most probable source of contamination.
 
im taking out all the river rocks today and iv got some stuff coming this afternoon that's ment to make rain water safe for fish , ill let you no its name ect when I get it , had 3 more looking sick yesterday all sitting on the bottom so iv taken then 3 out put into hospital tank they are still sitting on bottom but today they are still alive so hope they make it , and no there was nothing left in tank after salt water was used , when I got it ,it had leak so I had to fix that so tank was filled and refilled a few times so it had good wash out ,
 
Were the river rock used in any landscaping, etc... before you put them in the tank?

Usually river rock aren't a problem (I have them in my pond), but if they had been sprayed with weed killers or insecticides a lot, it could leech out and do damage.

Best bet on river rock is straight from the source or landscape supply - not scavenged.
 
got rocks from landscape supplys the stuff iv put in tank is called tropical conditioning salts and some armour coat lets hope that fixes it ,, iv take some rocks out but not all
 
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