re clown plec/platy/stocking levels

Question
hello karen,
Thank you for your response, it was very helpful and encouraging.Regarding some of your questions:
My ph is 8 and is stable. i have bought amquel and will give it a try.im reassured that my neons and so on,although prefer soft water are ok.they are active and seem happy.however i will over time take your advice and add more neons and rasboras,they will be happier in a larger shoal.
I found my clown plec this morning, looking well,smooth and rounded,and eating some algae.I was worried as i couldnt find him,having looked everywhere.
regarding my platy.he has no other symptoms,hes active,swimming and eating well.it simply looks like ive spilled wax on him.he is red with a black tail,and this growth goes across his side and into his tail.it looks pale orange in colour,grows slowly and seems as if its just been stuck on.The rest of his colour is still a vibrant red.none of the other fish have any symptoms at all.hes about 3/4 years old.he has no other marks and his scales look healthy apart from this. i read about fish pox but im not sure.
my water quality i assume to be ok apart from the nitrate in our water, i test and that seems to be the only problem apart from ph and some phosphates on occassion. i use easy balance but im not sure its effective.i change 20% of water every week to 10 days.I feed tetra pro and frozen brine shrimp, (and some broccoli they like about once a week)my tank is mature, about 6months old, but were transferred from another tank, i used the same water and filter media.that tank was three years old.im stuck as i dont know how to help my fish. none of the local vets have a clue.
many thanks karen
lisa

Answer
Hello Lisa!
Wow, that is odd. I have never heard of anything like nor have I ever had a fish have a growth on his side like spilled wax. But I do have one strong thought of what it might be-- Costiasis-- OR skin and gill flukes. A cloudy patch on the infected fish is one of the symptoms of both diseases. Both of these are parasites that attack the skin and gills of the fish. Do some research on these diseases to determine if your fish has this. It is so hard to diagnose a disease without looking at the poor fish. So I think it would be best if you looked into the symptoms and researched it to better confirm that's what your platy has.  Other than that I am with no clue as to what your fish may have. If he seems very healthy it may be nothing but a change in his coloration. He is a rather old fish and pale color is often a sign of old age.
Just watch him.  Insure his water is warm and clean.

I really hope this helps! If you have anymore questions, feel free to email me...

Best wishes,
Happy fishkeeping!
Karen~