i have recently cycled my tank using a goldfish which died then i put a black molly in which died over night i tested everything and found the GH over 200ppm and KH over 80ppm is this due to the tank being cycled??

I've never tested for GH or KH in any of my aquariums. To start making adjustments you are going to need a good knowledge of water chemistry. You will also have to make adjustments every time you do a water change. The following link may help you

http://aquariumpharm.com/faqs/faqs.aspx

ok would you have any advice as to why the fish keep dieing?

99% of the time it is poor water conditions that cause fish deaths. You have to remember that a fish tank is a living environment. I'm sure I'm not telling you anything you don't already know but You can't just fill an aquarium with water and expect things to live happily ever after. You have to create a safe living environment before fish will survive. That's why goldfish don't last very long when people take them home from fairs, they just plonk them in tap water and expect them to live. Thankfully, the practice of giving away goldfish at fairs has been mostly stamped out in the UK.

If you are suffering from fish deaths, the first thing you need to check is ammonia and nitrite. These two elements are highly toxic and will either cause harm or kill your fish if present for too long. If you can test for these and give us the results, then we will be able to advise

I fully agree with everything ofl has said

What is your pH?

my PH is 8.5

Are you sure. Thats very high even for oscars. is thats from your tap or tank. can you check both

sorry 7.5

deff 7.5

7.0 is the neutral level of pH. fish can tolerate variance between 6 to 8 or higher but should be keep stable. at pH 6 now and then PH 8 in 3 to 4 hours will definitely stressed your fish.

something that might be of interest to you is that if your pH is high, ammonia becomes more of a problem to your fish. fish can suffer a higher level of ammonia with a low pH of say 6. this is worst still if you have high temperature in your tank. 7.5 isn't that bad but I would check for ammonia. lastly i wouldn't recommend trying to change your pH.