Nutrition problems / ph issues in rockwool

Hi!

It is my first experience with hydroponics. I have few DP Powerplants growing in rockwool cubes. It's day 9 of vegging. I am running 2 1000wt hps 18/6. I am watering with drippers 15minutes each 6 hours (rockwool gets completely saturated). Water temp is 80f. I am using the tap water (EC is 170) and Canna Aqua Vega fertilizers.

Four days ago plans started to show signs of nutritional deficiencies. EC was 1,45 at the time. On few plantes lower leaves turned yellow than brown. The weakest plants are affected the most and I think they are going to die pretty soon if I don't change anything as 50% of foliage is affected. The new growth on bigger plants is fine and tops look good.

I feel that the condition is caused by pretty bad ph fluctuations that I have. I am trying to keep it in 5.2-5.8 range but it just keeps raising up to 6.8 overnight. Plants do use a lot of nutes. Yesterday I have changed the water and added less fertilizer than I normally do thinking that it would fix the problem. In 12 hours EC droped from 1,25 to 0,85. At the moment more leafs are dying.

Are they starving?
What can I do to heal my plants?
Is there a way to stabilize the ph?
Should I add more nutes?
Do I water them right?

Advices will be much appreciated!!!

The first rule in hydroponics is if anything looks wrong, change the res.

It does look like they are wanting food, but it could be any number of things. Your res temp is too high, there could be some nasty stuff going on in there, and therefore in your medium. Flush with some plain water pH 5.6, and measure the pH when it comes out. Same with before and after EC of flush water. That may tell you what's going on in your medium.

With that much light for 18 hours, they will need some food, as well as plenty of fresh air. Don't drip again if the cubes are still heavy with nute solution.

HTH