Platys not very happy.

2 of my female platys don’t look very well. They are getting thinner and are not eating. Then often stay near the surface or bud amongst the plants. No other fish seen affected. I tried using NT labs anti fluke and wormer twice every 2 weeks but it did not do anything. If you have any idea what this could be it would be appreciated.
I also have another problem. For the past few months in particular, there have been a lot of problems in my tank. You can go and look at the past threads I have made about these issues but here is a list: My guppies had what I think was callamanus worms which I treated but they ended up dying over the next few weeks anyway, probably because of the stress. I believe that these fish came with the worms and we’re just a dodgy batch of fish as they all died quite quickly. Then a few months later there was a problem with one of my fish having issues with their swim bladder. They were having to swim very hard to swim down. I managed to resolve this issue by feeding them some bloodworms which I believe helped as it is not very badly affected any more. Then only about a week after that, one of my rainbowfish developed something that I could not resolve. It was swimming like it was irritated often nearly doing loops in the water. It would often not move and then start darting around the tank. It died a few weeks later. And now there is this problem. My question to you is. Is this amount of issues normal, as I don’t think there any any problems with the water or tank? Here are some details.
Yesterday I tested the water and:
Ammonia: 0
Nitrite: 0
Nitrate: 10
pH: neutral-hard
dH: 16.8
The fish in my tank:
6 boesemani rainbowfish
8 lemon tetras
9 platys
6 guppies
The tank is 119cmx39cmx59cm
I had a fluval 407 and the tank is 25.7 degrees Celsius. I do a 50 percent water change every 1 week and dechlorinate the new water. I clean the sand. I do not use any plant fertilisers other tank some root tabs occasionally. I feed them a fairly varied diet of flakes, bloodworms and pellets.

What does their poop look like?
Are they eating anything?

If fish aren't eating well, do a stringy white poop, and lose weight over a couple of weeks, it's usually caused by an internal protozoan infection. Metronidazle is the normal medication but is unlikely to be available in the UK without a vet prescription.

Is there any aeration/ surface turbulence in the tank to keep oxygen levels high?
Do you add carbon dioxide (CO2) for the plants?

If you keep fish like guppies and other common livebearers from pet shops then these problems are common. If you find healthy fish in a clean tank then it's not normal to have these issues.

I have been observing them for the past 2 weeks or so and not once have either of them pooped out anything and no, I haven’t seen them eat anything. There is a spray bar at the back (I attached a video). I do not use any CO2. Are there any alternatives to metronidazole in the UK?

The UK and many other countries are cracking down on antibiotic use (mis-use) because of the drug resistant bacteria killing people and animals. I doubt you will be able to get anything to help without a vet prescription and it will be a lot cheaper to just replace the fish. However, don't add any new fish to the tank until we figure out what is going on. And don't add new fish to a tank until there have been no deaths or health issues for at least a month.

You could try adding salt but it might not help, especially if it's an internal infection. I would try to treat the fish in a spare tank if you have one. When you catch the fish, keep them in water and don't lift them out in a net. Catch them in a net and put a container under the net and lift the fish in the net. Then move it.

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SALT
You can add rock salt (often sold as aquarium salt), swimming pool salt, or any non iodised salt (sodium chloride) to the aquarium at the dose rate of 1 heaped tablespoon per 20 litres (5 gallons) of water. If there is no improvement after 48 hours you can double that dose rate so there is 2 heaped tablespoons of salt per 20 litres.

Keep the salt level like this for 1 to 2 weeks. If there's no improvement after a week, stop using salt and do small water changes to dilute it out.

The salt will not affect the beneficial filter bacteria, fish, plants, shrimp or snails.

After you use salt and the fish have recovered, you do a 10% water change each day for a week using only fresh water that has been dechlorinated. Then do a 20% water change each day for a week. Then you can do bigger water changes after that. This dilutes the salt out of the tank slowly so it doesn't harm the fish.

If you do water changes while using salt, you need to treat the new water with salt before adding it to the tank. This will keep the salt level stable in the tank and minimise stress on the fish.

When you first add salt, add the salt to a small bucket of tank water (2 litres or 1/2 gallon) and dissolve the salt. Then slowly pour the salt water into the tank near the filter outlet. Add the salt over a couple of minutes.

Ok, thanks for the help.