Please Some One Help I At Wits End

[wrighty.uk.gorl]

Hi can some one please tell me what wrong with my tank I have run a course off Protozin as my LFS shop recon i had velvet.
Reading about on the internet i seem to have the signs off flukes and currently running treatment for that.
But i really feeling i running round and round and i keep losing fish.

I have a 170l tank
ammonia 0
nitrite 0
nitrate 20ppm
ph 8

My molly i have stay at the top off the tank and tails are always down. One molly dies and gills had like red pin pricks over it but as said ammonia is 0. Lastly i have not seen my molly do a poop for couple days and a couple molly when going it clear and or colour off what they are eating. All fish are flicking but not very ofter.

Is you look close at the photo off the guppie you can see the gills are very orange is that velvet ? and what is wrong with the algae eater please

Sorry about the large images also the orange is not that bad on the fish had to take with phone camera and not come out to well but the gills are that orange

in the tank is 8 guppies
4 mollys
4 neons
1 plec
3 loaches
2 algae eaters

 

[Big_eyes]

Do your plants have a green slimy web type stuff growing on them?

 

[wrighty.uk.gorl]

Do your plants have a green slimy web type stuff growing on them?

No Nothing on the plants at all.

Will also add though it look like i going to loss another female molly any time soon it now laying on one off my plants with no intensions on moving any time soon