Help! What Should Nitrate Reading Be?

Do you know what your water company says (on its web site) that the normal nitrate level is in your tap water? You should try to get your tank water as close as possible to that, which varies widely from place to place according to where the supply comes from.

50 mg/l (or 50ppm) is the maximum permitted level in UK drinking water so it looks as though they are just saying they are complying with the legislation. My water company tells me that they tested the water for nitrate 8 times during 2013 (the last full year available) and the results varied between a minimum of 1.4 and a max of 6.9 with a mean of 3.1625.

This is my water quality report, does your company not have anything like this?

Those figures mean that for your tapwater you should have a colour on your tester somewhere between 20 and 40, but nearer the 40 colour than the 20 colour. Though to be honest, on my shade card there isn't much difference between the two. But the colour should be a bright orange red to red rather than pure orange (10) or orange yellow (5).
And your tank nitrate should be higher than that, in the definitely red shades, at the end of a cycle. Or if it is very high, the colour should be turning purplish.

It might be a groundwater problem. The South and East, being drier, would use more groundwater than the north and west generally. My up-to-date numbers, from North London, are min:20.8 avg:24.89 max:29.8. And I know that my lot do use groundwater.

I now think i have missed my window of opportunity, and am trying to balance empty tank. Despite 90% w/c on Tues, my NITRATE has risen to either 40 or 80 ppm not sure, OMG have just done same test on existing tank and it reads the same, fish are healthy so is that ok maybe? should i do tap water test again?

I did tap test this morning Sue, and sure enough it was 40 too, so not a lot i can do about it, Platties and Minnows are thriving on it so for now i aint gonna worry (supposedly my new year mantra) that won't last long especially as iv'e got residence in the new tank now 6 new Congos, so it's gonna be days of scrutinizing and counting lol.