Outdoor grow deficiency

Hi- outdoor grow, coots mix. Water only with pond water/rain water. Yellowing of lower leaves, purple stems (but maybe strain-grapefruit)
Any help is appreciated- thanks for your time!

Looks like nitrogen draw down from fresh compost

Rainwater is very low pH. I don’t know about your pond water. Not sure of your medium recipe. Maybe this will help.

https://www.kisorganics.com/blogs/news/basics-to-mixing-your-own-soil