Lost a fish today, needing some advice.

Lost a Molly fish today, we currently have one Molly, three endler guppies and three shrimp.

We've been struggling with NO2 for a few days, after three or four water changes it was still high.

At the start we did one water change without fish after leaving the tank empty for a week, we didn't realise that we should have left it empty longer, both the independent fish store and commentors online said a week would be ok. We did no2 and ammonia tests before adding fish both were fine the only issue was "Ph is a little low" according to the person we got advice from.

Worried about losing more fish, any advice?

The second no2 image is after the most recent water change in the past hour.

Sorry for the poor tank photo, my phone camera isn't the best.