Originally Posted by bozzzz
The tank is 100 L
We put tap safe in water and thats it WC about every 2 weeks with about 20 litres
Water looks great and clear thanks for the info but should i do more changes if this carrys on mate
A 100 litre tank is equivalent to around 26 gallons. Initially there were 4 molly and 9 guppy. The only thing i can see from all the data is still the effect of the initial cycling. The tank would only start to cycle when the fish went in, and this probably affected them. Molly as I mentioned are particularly sensitive to any form of nitrogen (ammonia, nitrite, even nitrate). Even though fish seem to survive the cycling, it can take a toll and weakens them considerably.
Water changes should be every week, without fail, and I would change about 1/3 of the tank. If the tap water hardness and pH is close to the aquarium's, this will be fine. Vacuum the substrate during each water change (assuming you don't have live plants, if yes, then you can leave the substrate).