My cory cats are dying :(help!

[GouramiCichlid]

I've had my tank setup for about 6 months now and I've never had a problem with fish dying (only time a fish died on me was because it was eaten)
I have a forty gallon breeder with a 350 Marineland power filter and quiet flow 40 HOB filters
I have around six mollies( temporary girlfriend didn't have anywhere to put so she left it in my forty)
I also have a school of cories (or should I say had) around 6-7 down to four
I have three loaches one zebra two clown
(I'm aware that the clowns will grow this is a temporary tank for them)
One rapahel cat and four bumblebee cats south american if you are wondering I made sure that they weren't the.Asians before buying (three are Frys or actually about a month or two old one is fully grown)
I also have a gold gourami and golden wonder killi
I do 20% water changes twice a week(I actually had to do three water changes recently consecutively. because my nitrate got to 40) what's happening to my cories I also had one of the mollies die.

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[lilme]

is your goramie picking on them?

 

[GouramiCichlid]

No he's extremely docile he just swims in the middle and occasionally rest under some rocks actually sometimes the.loaches chase.him lol

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[Pamiam]

If your nitrates were high, that could have killed them.
http://www.pinterest.com/pin/create/extension/

 

[Ricky 1]

Could be your parameters are not right or they can easily starve if your not feeding enough............

 

[MMantelli]

What exactly are all your paramaters 40 isnt to bad by the end of the week how often and how much watee gets changed I do 50% weekly on all my tanks and even my overstocked mbuna tank never goes over 40 also how much good is left on the substrate when you feed

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[GouramiCichlid]

Sorry for late response was at work
My.water parameter is
Ammonia either 0 or.25 I can't tell the difference
Nitrite is 0
Nitrate is either 40 or 80 seeing as they are both red its hard to differentiate between the two
My ph It says it's at 8
I never have any food left on the bottom I do about 40% weekly
I feed them.sinking shrimp pellets algae wafers and blood.worms Im pretty sure I'm feeding.properly

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[MMantelli]

Sounds not too bad up the pwc to 50% a week do you have any pellets for them

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[GouramiCichlid]

Yah lol shrimp

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[GouramiCichlid]

Still don't know why They are dying though

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[MMantelli]

Are there any sores or sunken bellies or just anything physicially odd?

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[GouramiCichlid]

Actually the first one that died was.spinning like.crazy before he.died.the.second not sure the third had.a bloody face assuming some attackedit at night not sure what nothing odd about.their appearance

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[MMantelli]

Sounds like someones beating up on them. But with the stock you mentioned I dont see that as an issue unless you have a rouge molly. LoL anyways is there anything Sharp, pointy or jutting out of any of the decor?

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[GouramiCichlid]

Uh not sure I can send a picture

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[GouramiCichlid]

M

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[MMantelli]

Well I dont see anything Sharp ummm... How do there barbs around there mouth look? The one with the head wound look up hole in the head syndrome soo If they look alike If so that could be it. We will get.this figured out.

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[GouramiCichlid]

The barbs on their mouths look fine the gravel is smooth but I'm planning on switching to sand. No it didn't look anything like hole in the head the cory actually looked like something.had attacked it. I just had a balloon molly die about two hours ago D:
I'm starting to.think it just might be the fishes I did get them recently at petco/smart I'm thinking if it had something to do with water chemistry then my clown loaches would have been the first to go

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[GouramiCichlid]

All of my older fish look fine I actually forgot to mention but I have a black ghost knife fish that Came with the tank got.him at about 3 inches he's at 5 now

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[GouramiCichlid]

My three albino cories are just swimming everywhere from top to bottom and occasionally resting at the bottom

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[MMantelli]

From what I gather your tank sounds healthy it could veey well be the fish from the big Box Store. What do you use for a dechlorinator? Do you add any other chemicals to the tank?

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