Thanks for the replies............

I am a little anxious as the tank is going very well, and I am now out of N. I just eliminated BGA via blackout recently and the N was a big part of this.

Don't want to have to start over or for the plants to suffer.........

I will try and find some calcium nitrate locally (not sure where to buy it) or some flourish or similar.

Thanks for putting my mind at ease........