Unfortunately, I believe that if you are going to have to find some better soil (or make your own) or I am afraid that your plants are not going to make it. Prenuted soils are simply bad for mj and I truly believe that your soil is killing them. Tell us more about your situation and maybe we can help you find some alternatives. If you have a source for good natural rich soil you may be able to amend that.
Second, the probes that you put into the soil are really poor pH meters and are horribly inaccurate. And we generally do not measure the pH of the soil, but of the run-off. Do you have access to dolomite lime? This helps with thepH. As a side note, you really need to be watering your plants to runoff. When you water just the top part of the soil, it keeps the roots from growing to their full potential and growing deep.
Rosebud is right about not spraying the leaves.
Adding the extra lights had nothing to do with the condition of the plant--it is just coincidence that it happened at the same time. You will eventually need way way more light though, so you will need to work on getting the heat down. Temps under 80F will generally not cause problems, but they do like it a bit cooler. You may find it better to suck the heat out near the top of the space , rather than having the fan push air into the space.
I will tell you that this growing encompasses way more than just sticking some seeds from a bag in a pot and putting a few CFLs over top. Cannabis has some very specific needs and wants that are not optional. I encourage to do more reading so you know what it takes to bring a plant to harvest. It is about a 4 month process and the plant has different nutrient and lighting needs at differing stages of its life. You need to learn what these are and then look for what you are going to have to do to achieve this end. You are at a disadvantage since you cannot simply walk into a store and buy what you need or sit down at your computer and order what you need. We can help you out with alternatives in some cases, but some things are not optionable. We can let you know what those things are.
So, read up more so that you know what you are trying to achieve. Look for some better soil and let us know what kinds of things you have access to--there are a lot of natural things that can enhance soil--that is basically what organics is--feeding the soil so the soil feeds the plant. Oh and see if you can get a small oscillating type fan that blows on the plants all the time. This helps move the air around and helps strengthen the stems for those big buds you are going to grow.