This may be a bit late for you, but will be of benefit to others.
Last year I lost 11 barra @ 1.5 kg to Cyclone YASI. (no power for 36 hours)
I replaced them this year with 20 x 7" barra and broght them up to ~ 1.6kg. 'chainsaw' and I ate a couple for our 70th. Not long after 'chainsaw' returned south my barra started keeling over (homesick for 'chainsaw'
). AT 18c he kept telling me my temps were too low (in the tropics admit at lower level). Barra weren't eating for two weeks. I went to local aquarium shop and bought 300W 1000 litre heater for $85 .... even if I could get the 3500 litres over 20c it would be better.Arrived home and went to insert heater. Three on the bottom and a couple coming to me on top to help them. Now I'm no mind reader, especially with fish, but I just knew they wanted to be out of that water. Everything else, Oxygen, Ammonia, Nitrates and Nitrites were all in specs.
8 O'clock that night I made the decision to get the final 10 out of the tank and into the 1000 litre aquarium with my two 'pet' barra. (some of you will remember that I mass-murdered the other 48 of them with overdoes of salt). During the night I kept checking and removing one or two dead barra. By three o'clock the next afternoon I hade one left floating on the surface. Picked him up, with help of a cloth, and knocked him on the head. Not wanting to lose my two pets I rang Qld DPI and managed to get through to Principal Pathologist (fish diseases). Prior to going to the lab I drained my aquarium to 50% and threw in a couple of GOOD handfuls of pool salt and PLENTY of oxygen
Within 1/2 hour I was at DPI and we had the last fish on the morgue bench. Cut off pieces of the gill and under the microscope where he identified 'Ich' (aka White Spot). There was NO WAY I could see anything wrong with the barra by just looking at them with naked eye.
The Pathologist was confused as to how the 'Ich' was introduced to my system. I finally remembered that I'd bought a few 'golfish' from local aquarium shop for the fish pond. I managed to kill them TOO!! Within an hour they were dead. Forgot that a couple of months previously I had a Chlorine tablet in that pond to reduce algae. I fed ONE dead guppy in the aquarium and one guppy to the 17 barra. Ah! he said, that was the carrier.
Now knowing the cause, my goal was to save the two pet barra in the aquarium. My advice was to take the water to 10ppt salt and 30c. I'm lucky enough to live alongside a poolshop so every half hour or so I'd take a sample of water down to measure the salt. First time it was 2628ppm. She said "Your salts down a bit". After explaing that it was for my fish tank NOT a swimming pool we managed to conclude that my aquarium was ONLY ~2.6ppt. After about four trips I managed to get the tank to 11.5ppt and 30c (had to add a second thermometer to get that high).
I'm pleased to report that barra are now back eating (smackingly) and look really healthy (that real silver sheen that you only see on barra in salt water). Water has seen 50% change and salt level retained ~11.0 ppt. Tank is wrapped in polystyrene panels during night (ambient gets down to 14c) and removed during day.
Next week I'll do another 50% change and start reducing salt to 2ppt. (I want to put a blue gravel filtration bed in behind the tank so water exits top of aquarium into growbed full of blue metal and back into normal aquarium filtration system).
My two pets are around 400-450mm and 1.5kg. They will NEVER be bound for the table.
You know: NEVER NAME YOUR ANIMALS! These two are Malcolm and Rodney
HTH