Four fish dead, what happened

[RJS8540]

I got a call this evening from a very good friend, her voice I could hardly recognize as she way crying so hard. She had just lost 4 large tangs that she has had for nearly 10 years. I raced to her home with a volt meter and other testing equipment to find nothing out of normal. The only thing she did today was a weekly water change. She normally keeps salinity at 1.024 - 1.025. I read it to be 1.029. Would that swing be enough to kill 4 otherwise healthy fish?

[Painted skin]

That sure could.

[MARINECRITTERS]

Sounds like this is one of the problems you can't test. A specific gravity of 1.029 should not kill a fish, at least a healthy one. Try testing for copper, copper could of came from the tap, even with an RODI unit it is still possible to get through if filters are not changed often. It could be a major drop in ph, does she dose kalk, carbon dose or run a calcium reactor? Hydrogen sulphide could be an issue. If it forms over a long period of time and then all at once gets stirred up, that could be deadly. A voltmeter is not guaranteed to measure electric current, the shock would of "cooled" down by the time you tested it. An signs of disease, velvet is a silent killer.

[Slystone]

If the sg had bee quite a bit lower and was suddenly raised to that with the water change I think it could. If you google 'will 1.029 kill fish' you will find similar stories.

[MARINECRITTERS]

If the sg had bee quite a bit lower and was suddenly raised to that with the water change I think it could. If you google 'will 1.029 kill fish' you will find similar stories.

If the fish were healthy then 1.o29 would not kill them, maybe shock and slowly die of disease but not immediately kill. I have some fairly delicate fish and a while ago my ATO failed, specific gravity got up to 1.032 and they were fine.

[Painted skin]

high SG is not healthy for fish under prolong condition. Gradual increase will not have as much impact as much as drastic sudden increase and jump into high SG.

For someone to have SG 1.024-1.025 and prep a small percentage for WC and now tank is at 1.029, that prep water must had been pretty salty through the roof finally settle down to 1.029. What I like to know is what was that measured by a hydrometer or refractometer if it was hydrometer then it might be even higher.