Check out THIS, it might help ya.

I used white vinegar, 5% acidity, mixed w my water to help lower the pH a bit at first. I only used it for a week and it helped to slowly lower it a bit over time. I'm using pH Down from a hydro shop now. My pH tests were showing it took roughly one teaspoon vinegar to lower the pH of a quart of water 1 number. I'd still used caution when adding anything though.

Is that temp at plant height?

Do you have good ventilation and a fan circulating air in the grow area?

How close are the lights to the plants?

You're deff gonna need more lights soon. The sooner the better.

EDIT: Are you feeding the plants any nutes yet?