Hi after many years away from tropical fish i have just started up again,bought my self a tank 60lt pump,heater,filter pump all cleaned out put in coloured stones and lava rock,and sunken ship inside set it up and all looked well left it running a few days temp looked good every thing working fine, went with some water sample to shop to get it teasted first before getting any fish all checked out ok so i bought 10 guppy's did as they said and as i read in books flot them in the tank for 30 mins added water from my tank and let stand again for another 20 mins, netted them out and put into tank emptying water they camr in away, great all looked good till about 3 hours then went to bed got up next morning and all was dead? we dont know why. went back to shop and asked them if they know what was wrong and they didnt know,said it might be coloured stones or larva rock and i asked him for his advice he said start again from scrach and put sand in insted of the coloud stones, we bought some sand the right sand what they had stripped tank out cleaned it again cleaned allequipment put in sand and heater filter air stone re filled it and left it for another 3 days took sample in and had it tested again some thing as before every thing looked good so bought just 2 guppy's repeted the same way of interducing them and they looked good keeped my eye on them and as before with in 4 hours they acted strange and shortly after they died as well. was hopeing some one could throw some light in my problem. many thanks .... hobby57