some spots on leaves

Hello, have some spots on two of my three autoflowers, just on some leaves not all leaves. Here you can see a picture.

1)Growing indoors
2)I'am watering only when first inches of soil are bone dry. I use 2 gallon pots, and water every weekend.
3)Using soil mixed with perlite
4)It's 4th week now from seed

Can you tell me what these are? Maybe it's some deficiency and i can use biobizz alg-a-mic via foliar feeding?
http://www.igrowhydro.com/BioBizz-AlgAMic-1-Liter.aspx

any spider mites under leaves?

no spider mites, checked now, but i fed them with biobizz bloom nutes - half strenght than suggested yesterday, but i remember those spots there even before.
week before i gave them some veg nutes.

added one more pic, found that one leave looks like this

why you feeding bloom already?

they start to flower i think, 1st timer just learning, but can those biobizz bloom nutes burn? they are organic and only at half strenght.
trying to find some info, don't know what to do.

also - new growth today looks super healthy.
i watered them yesterday, but do you think i need to flush if it's getting worse?

in whole they look like this --------- >

today still nothing changing, can it be potassium deficiency?

you need to use bio veg and bloom at same time or just veg at a lower dose for flower.......

cant really see to much wrong with your plants so far.............