black pencil shading on chihlid

I am a worker at college and it seems like the only person who is worried about the fish here I really do not know much and I have gone though all the posts to find out if anyone else has had the same problems. We have two tanks 5o Ltrs each one is gold fish and one is tropical 2 female bettas,1 blue gourmi 1 yellow gourami, 2plecs and a yellow wot I thought was a parrot fish but is cichlid family. They have been here over a year.

The gold fish are fine they eat none stop and seem to recognise me as we have a feeding routine (when I say 'hello' fishes they come to the end I am at)

ON A SERIOUS NOTE the yellow parrot fish in my trop tank has got black spots like pencil shading and I am real worried I cleaned out half the water last week Thursday (as usual) I have Friday off then came to work today and hes got this black shading?? anyone got any ideas??

I also have noticed some tiny snails now. I have not put any snails into the tank, Of course I do not know for definate wot other people could have put in the tank but as far as I know these tiny snails have come from no where and they are eating the greenery WOT DO I DO?? can anyone help me. The students at college can speak for themselves my poor fish can not so please can anyone help yours Abigail

have you added any plants?
the snail eggs would have traveled on them.
take them out asap or you will be over run by snails!!!

have you tested the water?

Can you describe this 'shading' any better?
any chance you could tak e apic of it?

Oh thank you for replying. I have not put new plants in for 5 months they were cut greens in little pots (for a change ) from the pet shop I won't do that again. I also have a trunk with plants growing from it which has been in for over a year...instead of cleaning tank again is there something I can treat it with?? as I don't want to stress the parrot anymore than it seems it is (he is still eating and hiding in amoungst the trunk which seems to be his usual behaviour) but he has this shading like when you get a pencil and lightly shade on a piece of paper. I will try to do photo. thanks Abi

photo ....hopefully...

Here is my photo it is not great but you can see the shading on his face, I hope the flash of the camers doesn't freak him out too much.
Thanks again for help so far Abi

I think I found the big snail which is on the photo with one of the small snails (sorry about my standard of photography I am doing my best I am a youth worker not media tutor or photographer or even fish expert ) so thanks for your ideas Abi

I have decided to call him Brian like Brian snail (memories from school days)
cheers Abi

sorry
i dont know what that is.
Any chance he could have scraped his head on something?
sorry