Deficiency?

New growth being affected usually means trace element/trace mineral issues..........think zinc and iron. P deficiency would present in older leaves first, not the new growth. Also showing slight calcium deficiency. Easily solved with a dose or three of soluble trace mineral mix (available from any decent garden centre) and applied to the roots. Do not apply to the leaves ....i.e. foliar feed.

Looks like PH to me. and Ca

Symptoms show low P and possibly a bit low on Ca pH is potentially the problem, too... Both Ca and P would be one of the first to have a problem due to low pH, though 6.0 isn't that low. If you use soilless fertilizers, it's right where it should be. this is where understanding how much you provide of all the nutrients can help diagnose.. if you know it's gotten pletny of P as you fertilize, then it's more likely lockout of some sort. Otherwise, it's just a guess all the time and the diagnosis won't be as confident.

pH problem at 6.1 but it's too much magnesium and calcium????? They are both cations how can you overload on cations and be at a pH of 6.1 .......... If the balance of charge in a medium is 6.0 then it means you need to add more Ca, Mg, K, NH4, sodium and/or hydrogen.. 1300 µS/cm electrical conductivity and a pH of 6.1, you need to add more cations. Your current EC is high for the acidity level. Remember if was as simple as a P deficiency then it would present in old growth given Phosphorus's mobility. Your pictures are not great but it looks very much like new growth is primarily effected making it impossible to be as simple as P def.

Yep it's P also add some N

Hi mate the ph is aboit low for soil you want between 6.2 and 6.7.. Magnesium overload and caused calcium lockout as there both positively charged cations there competing.. Low pH.. Calcium def and possible manganese def aswell.. Good luck growmie...

Looks like early stage magnesium or light nitrogen deficiency, not phosphorus. Since you’re in Biobizz Light Mix and already using CalMag, try increasing overall feed slightly or add a touch more Grow for a week. Keep pH steady around 6.2 and watch the new growth if it stays green, you’re back on track