Strange Guppy Deaths

[Newbiesoulman]

hi there , could anyone shed any light on what is happening with my guppies , the guppies in my tank over the last 3 months have slowly but surely started dying off, I have had loads of guppies in my tank for a year nearly all of them were born in there, every thing was great, I was  getting some fry every few weeks , then three months ago I noticed that the females stopped having fry , some started to get really thin ( male and female ) and died , some looked great but still died , I have been getting one or more per day dying , I have been regulary doing 30 - 40 per cent water change each week , every thing in the tank is great apart from the dead fish
 
the tank is  about  180 L with plants in which are growing great .
 
the water is
 
ph 7.6
 
ammonia is 0
 
nitrate 0
 
nitrate 1.0
 
the other fish are
 
bronze cory 3
 
platies 12
 
mollies 8
 
4 young guppies left out of 20 - 30   - 2 male 2 female
 
the only thing I have changed lately is a brighter light ( led )
 
at the minute I am stumped at what to do , all the other fish are thriving, the  platies are having  regular fry , corys look great , mollies are great to ( but no fry ), thanks Eddy

 

[bluesword23516]

Maybe something from inbreeding? I am totally stumped. 
But a nitrate reading of 1.0? 

 

[attibones]

That's a lot of fish for one tank. Not enough cory and a lot of live bearing fish. How long have you had the guppies? Could be due to old age. You need like three more cory of the same species. 
 
Also confused about the 1.0 reading for nitrate. What test kit do you use?

 

[Newbiesoulman]

hi thanks for the replies , the nitrate is a guess , the kit I am using is a api one , its showing yellow ( 0%) but a slight tint a  of orange so I  put 1% probably lower than that tho to be honest , the litre size of my tank  was a guess as I got it made to fit the alcove in the living room ,
 
The size is  40"  wide x18" high x 15" deep
 
the water temp is 77  ( is this ok )
 
I will get some more bronze corys this week,  anyone know how many more I should get, to fit the tank that is , Thanks , since I was last on here , one more has died , Thanks Eddy