I will look on-line and see if I can find a place that will ship Melafix and a test kit internationally. Sweden, right?
Here is what the Melafix bottle says:
"Antibacterial Remedy for Fresh and Saltwater Aquarium Fish. Rapidly repairs damaged fins, ulcers and open wounds. Fin & Tail Rot, Open Red Sores, Open Body Wounds, Eye Cloud, Pop Eye, Body Slime and Mouth Fungus." Here's what it looks like:
Their website is www.aquariumpharm.com and telephone is 800-847-0659.
Wow! That is a lot of money! Maybe you could contact Snowie, another member here on the forums. I believe she is from Sweden too.
Maybe she knows of a place where you could find one for less.
It's hard to say whether your fish have fungus or fin rot. Seems to me like you don't really want to add more meds but will if it's necessary. I don't want to tell you what do to because it's your choice, but if I were in your position, I would probably add Melafix and see if that helped. The problem is really with your water, not your fish. If you treat them with another harsh med, it could weaken them even further and leave them open to other diseases. It's up to you, do whatever you feel comfortable with.
A mechanical filter is a filter that sucks water through a sponge and/or carbon to remove stuff from the water. A biological filter is a usually just a sponge that collects the good bacteria that will eat the ammonia, and does not remove anything from the water. And you don't sound dumb. I didn't know any of this until I came here. This site has helped me so much.
White/stringy poop is an indication of internal parasites (so I've read.) But don't be alarmed because my swordtail had this in the beginning too. I was going to treat for parasites but decided against it. This was 6 months ago. I think maybe it's just a side effect of the stress he's going through. I'd give it some time and just keep watching.
My fish tank is at work. I have the light on almost all day, in total probably about 7 hours. My fish light at home is only on for about 4 hours. This is one of the things you'll have to figure out on your own because everyone will tell you something different.
You're welcome! It feels good to have the knowledge to be able to help someone . . .