Problem 4 weeks into flower

Hi, This plant has featured in these forums a few times. She's a power plant 4 weeks into flower. Growing in soil, PH 6.5. Using bio-bloom ferts. Some leaves, starting at the bottom are going yellow eventually turning completley yellow to a lime greeny sort of colour. I watered 2 days ago with 3 m/l of bio-bloom and a quarter of a tespoon of epsom salts in a liter of good old H2O. I thought it would be an MG problem as the veins on the leaves were still green as the leaf yellowed. I hope to hell it is and I hope I haven't given her too much because I've done the salt lockout prob before. Any help much appreciated

Okay, no more magnesium. That's not your issue and you could end up shooting yourself in the foot.
Plae green-yellow is nitrogen def. It's common late in flower and not something to be overly concerned with as long as you are within 3 weeks of harvest.
I seem to remember that PPP is a 8-9 week finisher, so a single foliar feed with a grow nute mixed 1/2 strength should help keep it from getting real bad.

I'm more worried about WHY you are seeing N def that bad, that early, with symptoms of other micro lockout... Check the runoff pH of your soil. I suspect it's not where it should be, and/or that you have a salting problem that will require a flush.
How to flush:
Check runoff pH.
Let's say it is 6.0. Make a jug of plain tap water adjusted to 7.0 to bring the soil pH UP.
Pour 3x the volume of the pot, in equivalent volume of water, yikes that's a terrible sentence, through it.
Then finish by watering with a bloom fertilizer at 1/2 strength and pH 6.7.
You are adding the N with a foliar spray hopefully, so you can use the bloom fert for the post-flush watering.

Thanks, I'll try what you've said. I picked up a info sheet for Bio-bizz products from my local hydro and it has a feeding schedule for the plants life cycle on it. I noticed that during the flowering stage I should still be using a small (1 m/l I think?!) amount of bio-grow aswell as the bio-bloom. I switched to bloom only and this might account for the early N deficiency.

My problem with PH is that I got one of those aquatic types which is probably really good and it ranges from Ph 6.2 - 7.4 but I struggle deciding which colour I've got on the chart. If I could find some product that was Ph 6.7 as standard, I could make a test tube up for easier comparison.

Thanks again your royal dankness