Cannot figure out which deficiency this is

I have an issue, i have two plants and one is exhibiting an extreme yellowing in the leaves while the veins stay green, but there is no red on the stem.

They had started to develop necrotic, black spots on the tips and soon inward; the leaf has since dried up and it came off w/o force today as I had inspected it.

It is Old growth, on the bottom; only fan leaves. The new growth is all green, except now I am noticing that towards the inside of the plant is has begin to curl leaves down & become very dark. Not necessarily green, but dark green/gray not a nice green, a worrysome one.

my pH has been skyrocketing recently, i adjust it to 6.0 everyday before leaving for work, and when I return home it is above 7.0.

Tomorrow I am changing the water/nutrient solution.

It is a DWC w/ fox farm for nutes.

I think it needs cal mag

is your water from a reverse osmosis machine

Sounds like a P deficency. When the ph is too high P becomes unavailable. Excess iron and zinc lock out P too. Lower your ph to 5.5 - 6.0. If you keep having ph probs try a ph buffered fertilizer. They work great. Good Luck!

buggs bunny said:

I think it needs cal mag

is your water from a reverse osmosis machine

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No. Tap water; there are two active airpumps in the tank as well to provide plenty of oxygen

tap water usually has a high ph,get these all in one nutes,with color coder ph monitor:http://www.hydroasis.com/hy/items.aspx?id=78&item=esu-greenleaves-nutrients,http://www.weedbay.net/overgrow-thebook/PlantTrouble/Merged.htm

If you use tap water it could be why you are having deficencys. I add Pond Water Detoxifier to the tap water. It removes chlorine, chloramines, heavy metals and anything else that would kill my Koi and Goldfish allmost instantly. No need to let the water sit for 24hrs either if you use the detox. It makes your water safe for growing too.