Welcome to BYC! First State Vet as lots of good stuff for sale, but some items are really expensive, so do shop around.
You should also know is that he is not a doctor. I'm sure he's quite knowledgable, but last I checked he did not have any type of medical degree
If you're curious in a morbid way, I did a post on the one that died, but beware, the pictures are xxx graphic rated.
https://www.backyardchickens.com/t/821240/internal-laying-ascites-and-eyp-very-graphic-necropsy-pictures
-Kathy
I have one that I have to drain every few months, but I also had one that died in my arms while trying to do it. This hen doesn't have that same swelling, it's just her breathing was very labored.
-Kathy
Lilypad, I thought about you yesterday when I found one of my hens "gaping". I have no idea what it could be, so I'm going to treat with antibiotis and wormer to see if it helps, but I fear it's something along the lines of ascites or EYP.
-Kathy
I use Kaytee Exaxt Baby Bird Food because it's soooooo much easier to get through the tube than crumbles. As for amount, a safe amount to give seems to be about 30ml per kg, but I do have one hen that weighs about 1kg and she can tolerate 120ml twice a day. When in doubt, start with 5 or 10ml...
If they aren't feeling well, they won'r eat/drink enough and this is what usially does them in and why I always tube feed when they stop eating and drinking.
-Kathy
That's the stuff, but it might be hard to get the right dose if it's a capsule with all those little beads in it. I'll have to look it up, but I think chickens get 10-30mg/kg.
-Kathy
Can you get medicine for tropical fish in the UK? Try http://www.ebay.com/itm/20-40-60-80-100-Tablets-x-100mg-Fish-FLUCONAZOLE-Antifungal-/271214493784
-Kathy
Disclaimer: I'm not saying that your hens have a fungal infection, but this is what a vet might prescribe if they did.