Nitrate and phosphate ratio

[tempestspace]

What is the importance of the nitrate / phosphate ratio? I'm struggling to get my nitrate down and my phosphate up. My nitrates is around 20-30 and my phosphate is reading at 0 on the hanna low range checker

 

[Spare time]

None. You just need a little of both and not too much of either. You can dose phosphate to fix the issue.