Problem with salinity fish won’t eat now.

So I did a water change today and I matched the salinity to 1.008 in the bucket however each time I added the 6us gal bucket to the 79gal aquarium the salinity of the entire aquarium went up by 0.001 so I stopped filling the tank and now the fish won’t eat, what have I done wrong that the newly treated water at the same salinity increased the entire aquariums salinity? Also the fish aren’t eating and acting a bit lethargic now.

What sort of fish?
Pictures of the fish and tank?
Why are you adding salt?

If water is evaporating from the aquarium, the salinity will increase and when you add new water containing salt, the overall salinity will increase.

Columbian sharks, because they need to be in brackish water theres only gravel in the aquarium atm and the heater.

Are you dechlorinating the new water before adding it to the tank?

There might be something in the new water that has upset the fish and has nothing to do with the salt level.

Increase aeration and check the ammonia, nitrite, nitrate, and pH.

I used reverse osmosis water with instant ocean, that should have put the GH and KH back into the water but when I checked the KH is slightly lower, I did use seachem prime to treat the water, the Salinity has returned to normal so the readings went down and the ammonia has spiked massively 0.5ppm so I used seachem ammguard an hour ago. That may be because they have stopped eating however the aquarium is large so Im not sure how about half to 3 quarters of a teaspoon of bloodworms could do that, the only other thing is I noticed is the temperature had dropped below normal to 23c so I increased the heater temps its usually between 25-26c, I carried out the water change because there was some type of bacteria or mould growing on ornaments so I took every ornament out. You can see that in the pics

The white stuff on the ornament looks like fungus. It usually grows on uneaten food.

Make the salt water up 24 hours before you use it so the salt can dissolve completely. Aerate the water while the salt is dissolving.

Make sure the filter is working properly.

Do you gravel clean the substrate when you do the water changes?

The bloodworm got trapped by that white stuff, thats how I found it, I fed them and they eat everything but that one just dangled there so I looked and saw the white stuff, I will be doing that from now on because the salinity was clearly all over the place even after 2-3 hours of mixing it, thanks, I did vacuum the gravel, I tried taking the uneaten mealworms out today but the vacuum wouldnt pulkl them out just water, the aquarium is only 1 and a half months setup so that was the 1st water change. I was told its cycled because I used seachem stability but after todays massive ammonia spike im not sure now as theres 0 nitrites and 0 nitrates still.

If it's the first water change the fish are probably stressed from it. Give them a few days to recover and do a water change at least once a fortnight and preferably every week.

Colin_T said:

If water is evaporating from the aquarium, the salinity will increase and when you add new water containing salt, the overall salinity will increase.

Click to expand...

Just in case you don't know this... (and apologies if you do )
If you do lose any water due to evaporation (even if its just an inch) it should must be topped up with pure RO before the next water change - same as in marine tanks. Otherwise the salinity will continually rise since water evaporates and salt does not.

Thanks I will follow your advise and see how it goes, do I need to put antibacterial treatment into the aquarium for the growth?