Phosphorus or MG deficiency? +PIC

This plant seems to getting worse, It had a N def which is now slowly fixing its self but the browning of the tips on older leafs is getting worse. Any idea's anyone?

Growing in coco, PH 5.7-6.0

Try adding CalMag.

What kind of water do u use.

I use tap water after its been sat for 36 hours, Thanks for the advice.

BuMp......

ill go with mag

looks more like this
Zinc (Zn)
Zinc plays a roll in the same enzyme functions as manganese and magnesium. More than eighty enzymes contain tightly bound zinc essential for their function. Zinc participates in chlorophyll formation and helps prevent chlorophyll destruction. Carbonic anhydrate has been found to be specifically activated by zinc.

Zinc Deficiencies:
Deficiencies appear as chlorosis in the inter-veinal areas of new leaves producing a banding appearance as seen in figure 18. This may be accompany reduction of leaf size and a shortening between internodes. Leaf margins are often distorted or wrinkled. Branch terminals of fruit will die back in severe cases.
Also gets locked out due to high pH. Zn, Fe, and Mn deficiencies often occur together, and are usually from a high pH. Don't overdo the micro-nutrients, lower the pH if that's the problem so the nutrients become available. Foliar feed if the plant looks real bad. Use chelated zinc. Zinc deficiency produces "little leaf" in many species, especially woody ones; the younger leaves are distinctly smaller than normal. Zinc defeciency may also produce "rosetting"; the stem fails to elongate behind the growing tip, so that the terminal leaves become tightly bunched.

I dont think its zinc, notice how the tips are brown in a v shape

I vote over water and over feed causeing lockout of N.
Amongst others stated above ie; Cg, Mg, Zn, etc etc

How often do you feed and water in the coco ?
Top feed or bottom feed ?

ya soil does look really dry. underwaterd most likly

These look like the first set of leaves on the plant and to be honest just pull them off the top of the plant looks realy good.I would take these of anyhow to force the top of the plant to become more bushy.At the very base of the plant where these leaves are shooting from will produce very little anyhow.Just flush the plant with water ph it first at around 5.5 and i would bet that the plants will improve....................................tyke....................................................................................................