Fluke solve is not ideal(ineffective) against internal parasites of this sort and most sorts. It surely doesn't treat hexamita which is what your Ram probably has because they are prone to it. But its a good one to have on hand if all the below fails. If the Ram was wild caught, only then I'd treat with fluke solve first because the fish may carry tape worms. These have complex lifecycles that require intermediate host. Shop raised fish almost never have flat worms unless they ran in the wild. Fluke solve treats some other external parasites but concave belly is not a symptom for such.
As an immediate home made med against that, get 500ml bottle of plain tap water or distilled water if you can. Put one full soup spoon of magnesium sulphate(Epsom salts) in it and shake to dissolve. Then soak only the portion of fish food you are going to feed each time, in that solution. Do that for 5 days at least twice a day. Make sure the fish in question eats it within seconds once you drop it in the tank, if possible. Do not feed any untreated food.
Do no expect immediate recovery. If the belly is very concave it will take time for the fish to recover but if it works you should be able to see within a week or two slight bulging of the belly, meaning the fish starts to put the weight back on. Keep the tank and water clean..
When you soak the food, make sure there's no excess water. Put tiny amounts of the solution just so the food is wet through but not dripping. You don't want to flush the goodies out of the food. Epsom salts taken by fish internally(not in the water column!) is proven scientifically to kill spironucleus vortens which is what we call hexamita. It's an opportunistic parasite common to south American fish and liverbearers. It causes concave stomach and fish lasts ages with it before it dies, if not treated, but its reversible so worth trying with the MgS04.
From the available in the UK meds, you can get Waterlife octozin. Its safe with any fish, plants or inverts. It treats hexamita mainly. It is basically a form dimetridazole, the cousin of metronidazole which is prohibited here because it has antibiotic properties.
The other one, which is a broad spectrum med, and very good, is Kusuri wormer plus. I am not sure if you have it in the UK but worth searching for. It kills snails and most inverts though but is harmless to any fish and will cover most every type of worm, parasite and even flukes. For hexamita it may need to be dosed twice. Its a good med for newly purchased fish when in quarantine.
