Ok don't fret I'll give you an easy rundow of what to do.
1) Your ph is very low because your co2 creates carbonic acid from combining with your carbonates in your (KH) This is Normal , the problem is your KH is too low so your ph crashes. You want to have a ph of around 6.8 or so.
2) To get your ph up and KH up you can use everyday normal household baking soda NOT powder. 1 tsp of baking soda in 10 gallons will raise your KH by 1 degree .
3) Check your kh of your tap water , it is probably low ( mine sits around 6.9)
Add a 1/2 tsp baking soda to your tank and then check your ph is an hour. Keep doing that until you get a ph of around 6.6-7.0. Plants need carbonates to live and the ph needs carbonates to stay up.
baking soda is safe ,cheap and contains no phosphates
4) 36 watts of pc light on a 10 gallon is ok you might have to add some fertilizer assuming you have no fish? best and cheapest is PMDD diy style from gregwatson.com ,read ALL his info it there.
Once you get your ph up to 6.8 you are set
Pss check out rexxgrigg.com for some really good planted tank info