Help appreciated.

[Delphinus]

You should try your hardest to match the temperature and salinities of the incoming and outgoing water, that will help ease your fish a little.

Also, fresh salt is quite caustic. Do let it mix before using it.

In an emergency, the best way to mix salt in a hurry is use a drill and a paint mixer attachment. This method of mixing salt oxygenates it or oxidizes it (or something - there's some in depth article about it you can read one day if you're interested, but for now don't worry about the theory). Anyhow with this method, mix for a couple minutes and then your water can be used right away. I don't know where you live but if you're in the south you're welcome to borrow one of mine, I have 2 that I use for just this purpose (emergency saltwater making) - they have never touched paint in their life.