When I had spider mites on the seedlings inside, I mixed up a tiny bit of Dawn liquid with water
and washed, then rinsed off the foliage. Had to do that a few times before the plants were ready
to go outside, but it did help. Gets rid of the aphids too. The plants began to look better right away.
I look for the tiny webs to identify spider mites.
I washed each leaf individually, rubbing my finger along the length of the leaf. If aphids, you will
feel a sticky substance on the leaves when doing this, feel the tiny aphids, and see the larger
ones.
Are the leopard looking spots only on the oldest leaves? If so, that may be a natural dying of the
outside leaves as the new center ones emerge. Of course, the natural dying spots are more of
a light yellow or such is the case from what I've seen.
The larvae of fungus gnats are almost transparent. Very hard to see and so tiny. About the length
of this dash. --- Double the width of the dash for the approximate width of the larvae.
If none of the above, I would guess that it is mold, mildew, or other fungus.
Other than that, are you watching to see if water is coming out fast from the bottom when you water
them. Sometimes the first run through of water will only go down the sides of the pots, and the plants
won't get the benefit of that. Have to repeat adding water until the bottom of the pots show a constant
drip drip.
Also, the potting soil may be the dark type and difficult to determine wetness. If you lift the pot and it
feels light, it needs water. Water one and feel the weight to get a baseline for judging the rest. I have
dark soil this year and missed watering a few sufficiently because of this. Now I feel the weight of each.