1. The water that you use on the plants has a pH straight out of the tap or source, and it has a different pH when you add fertilizer to it. The soil has a pH of its own. The Soil, Water, and Fertilizer interact and give you a 4th pH number, which is the runoff pH when you pour enough water into the pot so some comes out the bottom. You will become familiar with ALL those numbers as a grower, and get in the habit of testing them at the start of the grow and if anything goes wrong. If you are in hydro, you will be testing pH at least once a day. In soil, a liquid indicator kit is fine. In hydro, you will want to spend the $$ on a GOOD QUALITY pH meter, or stick with the liquid kits. A shitty pH meter (*cough* Hanna *cough*) should be used for nothing but shoving up the bunghole of the manufacturer. I've seen crops KILLED by failed pH meters.

2. Topping is removing the primary growing tip. It lets secondary growth (branches) get bigger. Pruning is a general term for cutting anything off a plant. Topping is a type of pruning. Removing side branches to focus energy on the main cola is another. Taking cuttings to make into new plants actually functions as pruning too. Topping gives shorter bushier plants but should never be done less than 2 weeks before flowering, or in flower.

3. No.

4. In soil, you don't need one. You can take your tap water down to the hydro shop and if it is a good shop they will be able to tell you on the spot if your tap water is too 'hard' for growing in. If they have 'live' displays of plants in a hydro system, they have a EC meter that they can give you a reading with. After that, you are golden.

That's a sick light, have fun with it. And Mandala has always done good work.