My goldfish keep dying

[popmandy]

HELP i had goldfish for years in my biorb the 30 litre one and i always have fresh plants in there also. I lost both my goldfish to old age a few months ago since then i have brought gloldfish from my local pet shop. They were baby small ones and young but died. I emptied the biorb cleaned it all out threw away the plants in case and got all new ones. I then purchased some new goldfish from another place again young ones and all 4 again have died?? I treat my water with aqaua+ and i have had my tap water tested at my local pet shop and theres nothing wrong with the chlorine levels etc they say my waters fine, so why have i lost 8 goldfish in a month im not doing anything different to what i have before, and the biorb is in a cool place in my house so the water doesnt get hot and on really hot sunny humid days i drop a few ice cubes in to keep the water cool. mandy