So, you have some crook looking fish, and are about to enter HSM.
Scenario 1: you have just put the fish in within the last couple of days and they have started kicking the bucket.
There are a few things that could be causing this:
1 Temps are a lot different than where you got them from. Sudden temp changes will affect fish health much greater than slow changes in either direction.
2 pH is a lot different than where you got them from. It may take a couple of days for fish to be upset by a pH different in your tank to the one they are used to.
3 Something nasty has made its way into the water. This could be as simple as a sealant you used or some little rascal dropping something in your tank. Spray drift, contaminated rainwater, inappropriate garden sprays used on your plants are a few suggestions.
4 There is not enough Dissolved Oxygen in the water (signified by gulping fish at the surface)
5 You are having an ammonia spike, which would result from feeding the fish whilst not having the necessary bacteria present to convert to nitrites and nitrates.
6 They have ich or fungus or some such like disease. Look for spots, marks, coating on the fish that are white, furry etc. Mostly this is caused by stress so have a look back at the first few suggestions. Fungus is present in the water at any given time and will tend to affect a fish when its immune system is depressed, not unlike ourselves when we are tired etc we get sick more easily.
IMHO, in a new system, the biggest killer of fish is ammonia levels going sky high without realising. Especially in cooler climates, it takes a long while to cycle up your system, so much patience is required.
How to deal with these problems?
1 Ask the hatchery what temp they have their tanks at, and research ideal temps for the species you have chosen. Don't jump the gun getting fish into your tank if you are not ready.
2 Use shell grit or calcium carbonate powder to raise pH and buffer your water from violent pH swings.
3 Get the fish out of the tank asap if you suspect this to be the case. Any clean water with a bubbler will do in the first instance. Add around 3 parts per thousand salt ie 3kg's in 1000 ltrs to help reduce the stress to the fish. Salt is a pretty good AP cure-all as we don't use antibiotics and the like.
4 Increase water flow, add bubblers.
5 Do a water change to get your ammonia closer to 1 ppm. You need some ammonia to get the cycling happening, so look at the ammonia toxicity chart in the useful info section on this board. remember to use rainwater or dechlorinated system water. And remember if you have chloramine as your treatment base, if there is 2 parts chloramine in your water, neutraliser will leave you with a 2 parts ammonia reading, and thus not help your situation.
6 Add 3 - 5 parts per thousand salt to your tank. Raise the temp to increase the speed of the life cycle of the ich.
And if there are any dramas, feel free to yell out and we'll try and get them back on the road to recovery!
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Have you check your water, with a dip strip, second are you using tap water. Tap water should be airatted for 48 hours due to chlorine. This will kill the fish and sometimes does not show up on a dip test.. You should run a your system for 10 days with cheap fish in it. To get your Bacteria going. 
)... and show us what you do...