pests issues

High, Most of my plants seem to have nute burn and that's all I thought it was. Until I just went in there again and I saw a tiny almost microscopic black spider. I hope it's not spider mites. I've looked at most of the leaves even under a microscope and I can't see any eggs or spiders or...

Hi guys, So I started my first indoor grow. I am using 300w mars hydro led lights in a 80x80x160 grow tent Canna terra pro soil Organic nutes(blood meal,guano, worm castings,fish meal,liquid kelp,molasses) Ph run off is between 6.3-6.9 on all of my plants. Only watering with chlorine free...