Yes.
Bloodworms and especially Tubefex worms sometimes are harvested from
toxic stagnant pools. They can contain the diseases and parasites that
live in these pools.
I was talking recently to a guy who got a bad batch and got sick fish.
Look at the blocks of Bloodworm if there is ice on top and the bloodworms on the bottom it can be a sign that they have thawed out.
I brought a slime scraping from a live Discus that was fed refreezed beefheart and it contained Strapticocal Bacteria.

Regarding the Metronidazole - I contacted Lissenhall Vetinary Hospital in Swords. They said they don't normally deal with fish problems as advised that I contact one of the specialist shops.

I told them that I got an over-the-counter remedy and it didn't work. I have now been advised to treat with Metronidazole. She was to get a vet to call me back, but needless to say, I haven't heard anything.

Can anybody recommend a vet that knows something about fish?

There is a vets in Raheny who should give it to you.

Just give him the dosage I gave you other wise he will only give you a little.

Have you tired salt bathing the Gouramis.

No, didn't try the salt bathing. I do have epsom salts if required.

I haven't seen any symptoms in the remaining 4 over the past couple of days. I'll do another water change tonight and keep an eye on them.

If I did get the antibiotic, I probably wouldn't use it until I see more symptoms.

The two Gouramis that died were from the same tank in the LFS so could just have had something that took a while to manifest itself.

I'll keep a close eye on them over the next couple of weeks.