Maybe you have thought of these, but things I would ask is:
Do you have driftwood in the tank? This will lower PH.
Do you have a whole house water softener or purifier or one at the tap where you get water from? If so this will work against you as well (could probably use outside tap they not usually connected through softener).
PH of low 5s sounds really low for water out of the tap I am sure it happens in places but that would be unusual. Maybe lot of Acid rain where you live
Anyway as for raising PH it is really easy to raise it temporarily, but if the water if very soft it will quickly revert to a lower PH. ALso keep in mind PH will normally decrease over time anyway without regular water changes to reintroduce buffering agents.
One things that helps keep PH higher is extra aeration.
Crushed coral, seashells, petrified coral, and limestone will all help raise your PH and will in general keep it more stable than just using PH raising chemicals.
If you got a lot of money you could also try something like this.
http://internetwatersupplies.com/phfilter.html
Adding chemicals that do nothing to buffer the water will not do much good, but if you can make the water harder and raise PH it should stay higher for longer. Want to make sure whatever solution you find though the PH does not swing up and down rapidly though that is usually a lot worse than just having fish in a PH that is less than their ideal range.
Hope it was some help.
and my pH won't raise above the low fives 
. What can I do?
. I just tested it and it came up a 5 even. It might be lower but thats as far low as my cards will go.
