Welcome fellow UK shrimp keeper!
I would think it would be better to remove the shrimp into the quarantine tank and keep them there whilst you treat the fish in the main tank and once you finish treating the tank and fish do a complete water change (maybe 2 a week apart for safety) before returning the shrimps. That would seem the best option though obviously the shrimp would need to be in the separate tank for weeks.
I'm not aware of any medications available for ICH that won't kill shriimp and/or snails. With neocaridina they probably will just about survive 30 degrees but you are pushing it close to the limit! I don't believe ich affects shrimps.
Re-posting here from The Shrimp Spot forum as I need help.
Help, 40 litre tank has a ich (ichthyophtyirius multifiliis) / white spot outbreak.
We've been able to separate the few surviving neon tetra into an emergency quarantine tank, with appropriate medicine for the fish. We had done this as we had noticed the issue practically too late as we miss identified the white spots as cotton mouth (which the tetra also have). We luckily quarantined the fish from the tank as the ich reached its second stage as most have matured and abandoned the fish. This has become an issue as even if the neon tetra do not survive the treatment, I cannot re-add them to the tank and I don't want to keep the tank's environment full of parasites.
Thankfully ich seem to not be able to effect the shrimp but the medicine we have for them is toxic to the shrimp and the plants in the tank, hence the separating of the neon tetra. I was wondering if there was anything I can do to the tank while the shrimp are still in the tank, as removing them isn't a viable option. We've been trying to get the temp of the tank to 30C and leaving it at that temp for an hour, however the tank's heater is verry slow and doesn't seem to be going up past 27C. From what I've searched 30C should kill of the ich without irritating the bloody mary shrimp too much (too many websites vary their recommended temp, so I wouldn't keep it above 28C long if we were able to get it that high) If anyone knows if there are any ich treatments or methods of killing ich that are safe for invertebrates and potentially plants I would love if they could suggest one.
For beginners and smaller tanks, I recommend glass aquariums because of their affordability and scratch resistance. For larger, more advanced aquariums, we recommend acrylic because it's lighter and easier to repair than glass.
It looks like the shrimp is about to moult.
I don't keep Ghost shrimp, so I'm not too familiar with how they look when going into a moult. But the white band along each joint is common in other shrimp when they start to moult.