I think there is a disease in my tank, but i'm not sure.
It's mainly affecting my larger fish, none of my little ones seem affected, or maybe i'm not noticing it as much.
Anyway, my angel fish's fin's seem to be tearing, same with my molly. Some are just rubbing against gravel and ornaments, my guarmi's seem to be losing there colour, they are turning brown on there head and my red tail shark keeps laying down, i thought he was dead a few times.

Have tried looking online, but every site i look at tell me different thing's. I don't want to treat them for a disease they don't have and risk hurting them.

Any idea's?

Sounds like a case of finrot too me, which could be a secondary infection to something else which is causing the lethargic behaviour and flicking against the decor, most likely external parasites. Are the fish showing any other symptoms such as small lesions, spots or heavy breathing?

Finrot can be caused by Aeromonas, Pseudomonas or Flexibacter bacteria. All are highly opportunistic and all exist in background populations within the aquarium. Almost all finrot infections are precipitated by stress, usually as a direct result of poor water conditions.

If you have a test kit, can you provide the test results for pH, ammonia, nitrite and nitrate?

Since several of the fish are infected it would be futile to quarantine any affected specimens, the whole tank will need to be treated with a proprietary medication such as eSHA Labs 2000.

In the meantime, I would suggest carrying out several large-ish water changes and cut out any feeding.

No, no other symptoms. it seem's that only my angels, gurami and shark that are bothered.
My shark is showing no other symptoms, he has more colour and energy than ever, same with the other's.
What my shark is doing, is he's laying down but the second my tetra goes near him, he springs into action and chases him, could he be just being devious?

I read that if there was something in the tank that my loaches would get it first because they are scaleless or something. But they are fine.

I'll do the test now

Got my dad to do it, my glasses have broke and i can't see that well!!
Anyway
PH is 6.0
amonia 0
nitrite 0,1
nitrate 18ppm

Is there something wrong with my water? Do i still do a water change? I did a 25% water change not long ago.

Your ph is too low and you shouldn't have any detectable nitrites, I would do a 25% water change now

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for the type of fish i have in, i was told that 6.0 was good. for my loaches, and angel's anyway. It was higher, but my loaches seemed to slow right down and generally be dull coloured, adjusted the PH and everything in the tank was brilliant, my angels had colour, my shark was black instead of grey and my loaches were the proper colour.
The Ph has been at this level for around 12 months and never had a problem.

Everything seemed to go wrong around the time i got my new plant. The plants were in a tank on there own, no fish or anything in with them, but i think it was just 1 big filter for every tank.
Can plants carry diseases/parasites?

Will do a water change tonight when my OH is around to help

The trouble with a low ph is that at a ph of 6 nitrifying bacteria are only 10% as efficient as they are at there peak at ph8.3. I would be aiming for between ph6.5 and ph7.5 which only looks a small difference but the ph scale is logarithmic so ph6 is 10 times more acidic than ph7

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If the ph has been like that for 12 months,I wouldnt worry.Stability is better.If you start messing with chemicals,its a pain in the bum.
Low ph is good,unless you want african cichlids.
If the fish are bred locally,they will be used to the ph.How often do you water change?Could it be aggression,causing the fin tears?

I agree with Holly, I wouldn't worry too much about the pH, so long as it is stable. Meddling with the pH could cause rapid fluctuations and upset the chemical balance of the aquarium, which in turn would only make the fish worse.

Several species come from water that is naturally acidic. Chocolate Gouramis (Sphaerichthys osphromenoides) come from water with a pH of less than 4.5.

no because they are splitting, and there's turning a brownish bronze colour. I have some medication, liquidizer or something i think it's called, aquatic place said it should do the trick. So gonna give that a go tonight.