Patchy Film On Rasboras

[Creature Seeker]

Tank size:
180 Litres
 
pH: 6.6 (this was lower than expected)
ammonia: 0
nitrite: <0.1
nitrate: <5
kH: <10mg/L
gH: <120mg/L
tank temp: 26 degrees

Fish Symptoms (include full description including lesion, color, location, fish behavior):
There is a is discouloured patchy film on some of the rasboras.  One is particularly bad and is breathing heavily and is patrolling the middle of the tank, which is unusal as normally the rasboras hide within the plants.  The other Rasboras seem to be nibbling at the patches on the affected fish.
 
Many of the rasboras have had a coludy film over there eyes for many years, which never seem to be a problem.

Volume and Frequency of water changes:
30% every month

Chemical Additives or Media in your tank:
None

Tank inhabitants:
x2 African Butterflyfish (Pantodon Buchholzi)
x1 Black Baby Whale (Brienomyrus Niger)
x10 Clown Rasbora (Rasbora Kalochroma)
x6 Elegant Rasbora (Rasbora Elegans)
x1 Empire Gudgeon (Hypseleotris Compressa)
x2 Striped Oto (Otocinclus Vittatus)
x1 Twig Catfish (Farlowella Acus)

Recent additions to your tank (living or decoration):
None
Exposure to chemicals:
None
Digital photo (include if possible):

 

 

 

[DoubleDutch]

I'd try to do some more WC's te coming time and have a look it get's better.

 

[Tongue_Flicker]

Judging from the growths on the plants i'd say your tank is kept too warm and too bright and something that looks like fungal patches now appear on your fish. Problem is that your farlowella and oto appreciates warmth while your rasboras and your black whale does not. Your two rasboras come from borneo where most patches of open water areas are shaded. Your black whale likes darkness to subdued lighting. You mixed different species from different areas with different biotope requirements and thus problems arise.

 

[Creature Seeker]

Thank you for your comments.  I am aware I have an ongoing problem with hair algae, which I am attempting to combat. 
 
Since my last post I have bought a larger tank and the Elegant Rasbora I thought was a gonna has make a spectacular recovery...however; there are still subtle patches on someof the fish and I have noticed that many of them have a cloudy film over their eyes.  The clown rasboras have had this for years, which I assumed has just their age, but now two african butterfly fish and two gudgeons have the same thing and a third gudgeon has one eye which is completely swollen.
 
Is there some kind of background bacterial infection going on here?...and if so how do I nip it in the bud for good?
 
Many thanks.

 

[Creature Seeker]

Any ideas?  Would love to eradicate my tank of infection for good!