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So I got a group of Clown loaches. They were supposedly acclimated to hard, high pH water. There were 5. Acclimated them by trickling fresh made batch of water slowly for many hours. Within 24 hours the first one appeared breathing heavy at the surface. He had a few white spots. Looked like ich.
Treated the tank with coppersafe. By a weeks end all 5 loaches were dead, in addition a bumblebee cat developed the spots, while the tank is treated and died. So far the cichlids in the tank are showing no signs of ich, or whatever it was....
What could have happened?
Of course I did water changes and took out any charcoal before treatment, (I usually don't use it as my water is clean as per city water reports). My water is pH 8 out of the tap and pretty darn hard. Parameters are generally good with no ammonia and nitrites and very low nitrates. I do keep a variety of plecos that breed well in the same water with no RO or any other treatment except some well soaked wood.
The seller is sending an other batch, a good fellow who I trust and done business with. I know others who bought this same batch and had no problems.

What is up? Oh, they did get pretty cool in shipping, I warmed up the bags in the main tank.

If your fish are being shipped or have to spend many hours bagged for some reason, the drip acclimation method can be counter productive. Ammonia can rapidly reach dangerous levels inside the bags. At the same time the CO2 levels increase. Co2 dissolved in water produces carbonic acid which lowers the pH below 7.0. The pH drop reduces the toxicity of ammonia. When you do a slow drip acclimation the fish are left in the ammonia laden water which quickly loses the excess CO2, pH rises above 7.0, causing the ammonia to become toxic.
All this is stressful, can cause damage to the gills and results in weakened fish more susceptible to diseases like Ich.

It is better to just equalize the temperature without opening the bag. Then perform the "plop and drop" acclimation method. It is less stressful for the fish. It is best to adjust the water in your tank to be similar to the seller's water before the fish arrive.

All this should have been done using a quarantine tank. None of your other fish can get sick if you quarantine new comers. Clown Loaches are notorious for their susceptibility to Ich and sensitivity to medications. Naked skin Catfish like your Bumble Bee Cat share this sensitivity to chemicals used to treat Ich.
Elevating temperatures to the high 80'sF soon after releasing the fish is often sufficient to prevent Ich from breaking out.