Yellowing / Yellow spots (pics)

How long has this problem been going on?
A week or so

What STRAIN are you growing?
Big Bang

What was the establishing technique? (seed or clone?)
Seed

What is the age of your plants?
About two weeks, give or take

How long have they been in the soil mixture they are in now?
Since they germinated

How Tall are the plants?
Between maybe 50mm and 125mm

What PHASE (seedling, vegetative or flower) are the plants in?
Veg

What Technique are you using? (SOG, SCROG etc)

What size pots are you using? (Include how many subjects to pot)
Quite small, not sure the actual size

What substrate/medium are you using?
What brand of soil mixture are you using?(percentage of perlite, vermiculite...etc?)
Using biobuzz Allmix I think

What Nutrient's are you using?
Using some biobuzz stuff, bio-grow

How much of each nutrient are you using with how much water? *Knowing the brand is very helpful*
Only a small amount, haven't added nutes for a few days though

How often are you feeding?
I tend to give a small top-up every other day or so, when the soil underneath is dry to my finger

What method of pH test was administered? Using Strips? pH pen?
Suspect it might be a ph problem, ordered a pen online. Before I've been boiling water, then leaving it sitting out for a few days

When was your last feeding and how often are you feeding?
Yesterday

What size bulb are you using?
250W HPS

What is your RH Factor? (Relative Humidity)
Usually between 30 and 40%humidity

What is the canopy temperature?
Between 70f and 85f

What is the current Air Flow? (cfm etc.)
Only pumping air out at the moment

Tell us about your ventilation, intake exhaust and when its running and not running ?
I just switch it on every so often at the minute, usually to cool it down

Is the grow substrate constantly wet or moist?
Nope

What water are you using? Reverse Osmosis (RO)? Tap? Bottled? Well water? Distilled? Mineral Water?
Tap water, boiled then left sitting for a few days

Are you using water from a water softener?
No

Has plant been recently pruned, cloned or pinched?
No

Have any pest chemicals been used? If so what and when?
No

Are plant's infected with pest's?
No

More pictures. I spoke to my local grow shop, and they said the issue was likely to be a lack of nitrogen. In truth, I haven't been feeding them nutes very often, but they're in Biobuzz Allmix soil. Put in some nutes with water yesterday, going to see how they get on.

They're still a little small to be needing any fert in that soil, so I'd say that it's a combo of overfert and not PHing your fert before feeding. First they got burned, and now they're starving.(nutelock, from low PH) The best way to save them would be to flush them with some PHed water, then transplant to a bigger pot with some new soil, and then don't give them any fert for awhile.

Thanks, going to get bigger buckets for them today. All the plants are starting to wilt now - whether that's related or not I dunno, but I hope I can save them anyway...