Yellowing pattern I have never seen

Hi! I'm encountering some kind of yellow spots/blotches on my new growth.
I have 2 plants with the issue:

one just started showing the yellow spots,
it did it too last run and it doesn't seem like it's really harmful, but I'd like to prevent it if possible.

the second plant showing the same kind of blotches is an autoflower I never grew before, but growing in the same soil mix.

Up until now the green always ended up "filling up" the affected yellow marks sooner or later (sometimes it takes one day, sometimes a few weeks)
So even though every leaves started with bright yellow marks here and there the whole plant still looks pretty happy


pretty much all new growth did that up until this point and it's growing really fast.
The most affected side shoots on my autoflower appeared and reached this size in 3days for example.

Could it be a more extreme version of the lime green you see in new growth when it's fast and healthy?

my best bet till I know and see more is MG deficiency, but I'm really not sure

Thanks in advance to all those who will try to help!

Do somebody knows what it is?
I had luck ignoring it so far, but I really don't know how Bad it could get...

I don't wanna seem too insistant, but I'm getting a bit worried and my post is sinking

What's your ph of water your using?
What kind of water you using?
How much water you giving at one time?

first thought is pH too

I use tap water at a ph of 6.5 and I don't water a whole lot because they only got in this size of pot for 2 weeks and I don't wanna risk overwatering.
I aim for it taking 2 days to dry out so like half a liter right now. It's increasing though.

I will try calibrating my ph pen.
I noticed I had to add more ph down to get to 6.5 recently. So maybe I got fooled and I'm watering way too acidic?
You think that could do it?

I use test drop kit for aquariums to test ph of water, changes color to ph level, good to have around incase pen acts up or isnt calibrated correctly. If ph is not within range you can lockout nutrients and plant will show deficiencies.

I'd be watering til you get a bit of run off, it's got full set of leaves and will need to be watered thoroughly til water runs out bottom of pot , then only water when pot is light and top soil is dry 3-4 days on average is what I aim for. But i only water if soil is dry if its wet then I wait another day or two and check again.

What medium are you growing in?

I'm using soil with soil release so throughout watering when roots don't occupy all the pot often cause overfert and salt buildup

I know slow release is not the top choice, but it's recommended by the "mandala seeds soil guide" And I can find it in europe.
I already had really good success of multiple ounces frosty dank harvests with this soil so I know it can work
(even though I'm starting to consider coco)
I think I have pool ph tester strips around I'll give it a go

Double check your pH...I think you'll find your answer there. Good luck.

thanks!