The GH and KH are way too low for mollies. They need the GH at 250ppm+.
What else is in the tank besides the mollies?
If you just have mollies, get yourself some Rift Lake water conditioner and add that to the tank to increase the GH to 250ppm. The pH and KH will go up as well when you use the Rift Lake conditioner. If you have other fish in the tank, let me know what they are before adding the Rift Lake conditioner.
Assuming you just have the mollies, and if you can't get any Rift Lake water conditioner for a little while, you can use salt (sodium chloride) temporarily to help them. Add 2 heaped tablespoons of rock salt or sea salt for every 20 litres of water.
If you live near the beach you can add some sea water to the tank. Remove 20% of the tank water and replace it with sea water.
When you do water changes you will need to add salt or Rift Lake water conditioner to the new water before adding it to the tank. The Rift Lake water conditioner or sea salt should be added to some tap water and aerated for 24 hours before it is added to the tank.
The bucket/s of tap water with salt or Rift Lake conditioner should be dechlorinated too. If you have chlorine in the tap water, you can dechlorinate it just before adding the salt to the bucket/s of water.
If you have chloramine in the tap water, then dechlorinate it about 30 minutes before you add the water to the tank.
-------------------
All three mollies appear to be skinny and I would say they have intestinal worms and possibly gill flukes. Common livebearers like mollies, guppies, swordtails and platies are riddled with worms and gill flukes. They get them at the fish farms and these parasites cause the fish to lose blood and weight. Long term the worms will eventually kill the fish.
I would deworm the fish and see how they do. You should also feed them more for the next month. The extra food will help them produce blood so they don't die from anemia.
-------------------
DEWORMING FISH
Intestinal Worms like tapeworm and threadworms cause the fish to lose weight, continue eating and swimming normally, and do a stringy white poop. Fish can do this for months and not be too badly affected. In some cases, fish with a bad worm infestation will actually gain weight and get fat and look like a pregnant guppy. This is due to the huge number of worms inside the fish.
Livebearers like guppies, mollies, swordtails & platies are regularly infected with gill flukes and intestinal worms. If the fish are still eating well, then worms is the most likely cause.
You can use Praziquantel to treat tapeworm and gill flukes. And use Levamisole to treat thread/ round worms. If you can't find these medications, look for Flubendazole, which treats both lots of worms.
In the UK look for:
eSHa gdex contains praziquantel that treats tapeworm and gill flukes.
eSHa-ndx contains levamisole and treats thread/ round worms.
NT Labs Anti-fluke and Wormer contains flubendazole.
Kusuri wormer plus (contains flubendazole) - sold mainly for discus, comes as a powder which is quite hard to dose in smaller tanks
Sera nematol (contains emamectin)
Remove carbon from filters before treatment and increase aeration/ surface turbulence to maximise oxygen levels in the water.
You treat the fish once a week for 4 weeks. The first treatment will kill any worms in the fish. The second, third and forth treatments kill any baby worms that hatch from eggs inside the fish's digestive tract.
Treat every fish tank in the house at the same time to prevent cross contamination.
You do a 75% water change and complete gravel clean 24-48 hours after treatment. Clean the filter 24 hours after treatment too.
Do not use the 2 medications together. If you want to treat both medications in a short space of time, use Praziquantel on day one. Do a 75% water change and gravel clean the substrate on day 2 & 3. Treat the tank with Levamisole on day 4 and do a 75% water change and gravel clean on day 5, 6 & 7 and then start with Praziquantel again on day 8.
The water changes will remove most of the medication so you don't overdose the fish the next time you treat them. The gravel cleaning will suck out any worms and eggs that have been expelled by the fish. Repeating the treatment for 3-4 doses at weekly intervals will kill any worms that hatch from eggs. At the end of the treatment you will have healthier fish.
