Added open-sans, which I use on my website

pgf-gl.tex

\documentclass{minimal}

\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}

\usepackage[default,scale=0.95]{opensans}
\usepackage{mathastext}

\usepackage{pgfplots}
\usepgfplotslibrary{external}
%\tikzexternalize 

\definecolor{GR}{RGB}{60,170,70}
\definecolor{C1}{RGB}{170,70,60}

\begin{document}
  
\begin{tikzpicture}
	\begin{axis}[xlabel=Time (weeks),ylabel=Individuals,
			width=12cm,height=6cm, ymin = 0, ymax = 50,
			xmin = -0.05, xmax=26.05,
			ymajorgrids, ytick={10,20,30,40},
			axis y line*=left, axis x line*=bottom,
			tick align=outside,
			axis background/.style={shade,top color=GR!5!white,bottom color=white},
			y axis line style={white, line width = 0.0001pt},
			x axis line style={black!60!white}
			]
		\addplot[color=GR,mark=none,ultra thick] coordinates {(1,8) (2,9) (4,7) (5,13) (6,12) (8,18) (9,17) (10,22) (11,41) (12,32) (13,24) (14,21) (16,21.5) (21,19.4) (25,21.02)};
		\node[coordinate,pin={[pin edge={GR,thick,densely dotted}]below:{\color{GR}Control}}] at (axis cs:16,21.5) {};
		\node[coordinate,pin={[pin edge={black,thick,densely dotted}]45:{\textbf{bloom 1}}}] at (axis cs:11,41) {};
		\addplot[color=C1,mark=none,ultra thick] coordinates {(1,4) (2,3) (4,5) (5,7) (6,9) (7,8) (8,12) (9,23) (10,38) (11,34) (12,35) (13,33.2) (14,27) (16,25) (21,24.4) (25,24.9)};
		\node[coordinate,pin={[pin edge={C1,thick,densely dotted}]above:{\color{C1}Treatment}}] at (axis cs:21,24.4) {};
	\end{axis}
\end{tikzpicture}

\end{document}