small spots and discoloration in seedling is this a concern *first time hydro grow*

I'm new to growing and new to hydro, I've got a 5 gal dwc set up and my ph is fluctuating like a mother so I have to keep adding ph down. Any suggestions with that would be awesome, but my main concern is a slight discoloration and a couple little yellow spots on the first real leaves. I have been looking around on the forums here and couldn't find anything that matched it really. I have 3 seedlings in the same bucket for the time being and I'm currently flushing them bc my biggest one started to get a little nute burn and now she's doing fine and this one is the only one that had this problem. Idk if it will help but the strain is kush from bc bud. Sorry for the crappy resolution all I have is my phone though, thanks for any help and Happy Growing!

Cal mag def
whats your ph and what kind of your nut!?

Okay thanks a lot i actually just added some calmag earlier. I try to keep the ph at 6.0 but it keeps jumping up to the 8.5 range so every couple hours i have to add ph down. I use pureblend pro and liquid karma, cal mag, root zone conditioner (mainly for some root rot I've been dealing with on my tomatoes and peppers in different bucket), and rootbastic