All the catfish, the neon tetras and the loach have a pretty low tolerance of salt, but the rest have a much better tolerance of salt- i'm not sure about the newt and the snail though. You should move the snail to the fry tank (the newt could eat the fry though so don't move it just yet).
You will need to get a small sponge filter for the cory fry tank, if you don't ammonia will just build up in the tank and kill the fry off, without any filtration the beneficial bacteria responsible for controlling toxins in the water will not survive. If you are worried about the fry getting sucked into the filter, then you can cut up a bit of fine netting and put it over the filter intake (i've seen many people do this before with success)

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With the stocking of the tank, i have to warn you about a few things- pim pictus catfish are predatory fish and as yours grows it will become capable of eating quite a few of the fish you are keeping in the tank (like the neons and platys), so you should either rehome this fish at some point or get it a decent sized tank of its own with more suitable tank mates;
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Do you know what type of pleco and loach you have? There are hundreds of different types of pleco's and loaches, varying massively in size and care, so its very important to know exactly what type of pleco and loach you have if you are to look after them properly

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Do you know what type of newt you have as well? Some newts are capable of eating fish when they grow large enough, and may need area's in their tank above water level to bask on etc.
What are the numbers of all the fish you have and how many gallons/liters is their tank

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With the salt, 1tsp per 10gallons is good- if you can get hold of the med though, Waterlifes Protozin is very good. On second thoughts though, since you have so many low salt tolerant fish, it is really the best option to find a chemical anti-whitespot medicine (like Waterlifes Protozin) that will kill off the ich

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