Let’s find horizontal asymptotes with help of the limits of this function at x->+oo and x->-oo
$$\lim_{x \to -\infty}\left(\frac{\frac{1}{4 \sqrt{5}} \log{\left(\sqrt{5 \tanh{\left(x \right)}} + 2 \right)}}{2 - \sqrt{5 \tanh{\left(x \right)}}}\right) = - \frac{\sqrt{5} \log{\left(2 + \sqrt{5} i \right)}}{-40 + 20 \sqrt{5} i}$$
Let's take the limitso,
equation of the horizontal asymptote on the left:
$$y = - \frac{\sqrt{5} \log{\left(2 + \sqrt{5} i \right)}}{-40 + 20 \sqrt{5} i}$$
$$\lim_{x \to \infty}\left(\frac{\frac{1}{4 \sqrt{5}} \log{\left(\sqrt{5 \tanh{\left(x \right)}} + 2 \right)}}{2 - \sqrt{5 \tanh{\left(x \right)}}}\right) = - \frac{\sqrt{5} \log{\left(2 + \sqrt{5} \right)}}{-40 + 20 \sqrt{5}}$$
Let's take the limitso,
equation of the horizontal asymptote on the right:
$$y = - \frac{\sqrt{5} \log{\left(2 + \sqrt{5} \right)}}{-40 + 20 \sqrt{5}}$$