Re: Help please fish dying. Nitrates in tap water?
#2
I'm afraid the shop has given you very poor advice as that is too many fish for a 40L and it's too small for mollies, unfortunately.
Regarding the nitrate reading, the legal limit in the UK is 40ppm, so it won't be higher than that from your tap. You can find out how much is in there by checking the water quality report for your postcode area on your water supplier's website. The level in the tank, however, may be very high as the tank is so overstocked. The API nitrate test is hard to read at/above 40ppm and is very sensitive to being done precisely as per the instructions, particularly shaking bottle #2 very vigorously.
Check your supplier's site and post back the result.