I've had spidermites and I've had cal mag probs
Cal mag is more lightening of leaves with green veins and
Spidermites make rust coloured spots
As well is what I got
Here is another example
They are very difficult to identify if you have an inexperienced eye, but you can see them when you’re motivated, and sick plants motivate you.
Spider mites like warmth (over 85 degrees) and they like a dry environment. That is why they are usually an indoor garden problem, but they can occur outdoors as well if it’s hot enough.
What They Do
They generally live on the underside of leaves, and that’s where you’ll usually see them. Females lay eggs on the plants and they hatch soon after. After hatching they feed for a few days then go into a new stage. The nymphs feed and then molt again into adults.
They have a quick life cycle, which means they can populate quickly.
All that feeding damages your plants. They cause damage by puncturing the leaf walls and sucking out enzymes. This weakens the plant and can cause death.
How You Know You Have Spider Mites?
There are several signs to indicate that you have spider mites. White dots will appear on the top of the leaves. They also make fine webs that are visible to the eye. If you mist the plants the webs sometimes show up better.
Spider mite webs
If left long enough the leaves start turning brown and dropping off.
Spider mite damage
Tiny white dots under the leaves are the eggs, which means you have mites.
Last, if your eyesight is good or if you use a magnifying glass you can see them.