I would suspect the lionfish in that size tank and it's actual current size wasn't bothered.Qt was 10 gallons mostly because the fish were small
The tank was set up a day prior to the fish
The salinity of the established tank is higher about 1.021, the established tank has been running for about 2 years
I appreciate the help
The Tang being a highly active powder blue probably was still stressed. Them coming straight from shipment to shop to you without a gap probably didn't help with such a finicky fish.
Good LFS typically will keep the fish in store for a week or 2 which can give you the peace of mind that they settled and started eating before moving again, so maybe find out if they offer this. Some extreme LFS will do a quarantine period prior to you even seeing them which is even better.
I lean of the same view as others. The fish load was high (not from you feeding but from what they had already consumed). Ammonia started to rise and wat bacteria was on the sponges wasn't enough to deal with this level of load. A tank twice the size would of naturally had half the ammonia rating which would of been more ideal.
The factor the lionfish went is what makes this seem more than case. There usually super hardy things.
Please get more people's opinions, but I would get a bit of rock that's suitable and place it in your main tank for a week to be 'seeded' then move that over to live in the QT tank as a hiding place and as biological filtration. Doesn't need to be much.
Then with a 10G aquarium I would bring those size and type of fish in 1 at a time, focusing on there needs (tang = herbivore / lionfish = carnivore). Otherwise your dealing with a lot.
Interested to see other people's view on this. I sometimes move my friendly regal damsel I to my QT when I get a new fish if there a rather skittish species (blenny / royal Gramma etc).
Are you fairly new to the hobby, or had experience and this is a suprise? Keep your head up.
- Paul