Ich or fungus?!

[LeaH85]

Most of Scotland has very soft water but there are areas where it's harder.

Scottish Water will tell you what their lab says. They do make it a bit complicated though.
Load this page

Water Quality Search - Scottish Water

Water Quality Search

www.scottishwater.co.uk

then enter your postcode in the box. That will tell you your supply zone - make a note of the name.
Next load this page

Water Quality - Scottish Water

Water Quality

www.scottishwater.co.uk

and download "water hardness data 2019" (as that's the most recent year). This will contain a huge table. Across the top are the various units for measuring hardness, look for two columns - 'hardness as mg/l CaCO3' (this is also called ppm) and 'German degrees' (this is also called dH). Now go down the supply zone column till you find yours and note the numbers in those two columns.

Once you get there, you'll know your hardness in the two units used in fishkeeping

28.56 and 1.60 is what I found

 

[Essjay]

I presume that's 28.56 mg/l CaCO3 (ppm) and 1.6 German deg (dH). That's very soft water. Platies need much harder water.

But get the ammonia and nitrite under control first, then talk about what to do next.