Brita won't take out any dissolved solids so that won't really work. If the spring water is run through a distillery or
RO system which it often is to make it taste better then you can use that without a problem (in any case it will probably be softer than what you are getting out of the tap. I use rainwater sometimes but in Jacksonville I probably wouldn't & most folks tell you not to.
Driftwood & peat moss (in the filter) will both lower your pH but will make your water have a yellow brownish color (this is just the tannic acid given off by either of those & won't hurt the fish a bit). In fact many amazon fish like a bit of tannic acid in their water since it simulates their natural habitat (depends on the species though). If you collect your own driftwood be sure that you look up how to sterilize it before you put it in your aquarium. You won't want to soak it quite as long as the directions say to get out all the tannic acid because you will want some to leach into your tank. You can do part of the water logging process in the tank by weighting the driftwood down with rocks (this is probably not recomended but I have done it)
Another option is to go to your fish store & buy a couple bunches of hornwort & throw them in tied to something so they won't float all over (they are a rootless plant that takes up a good amount of fish wastes). Then you can run a
DIY CO2 system which will bring down your pH also. This is not a quick fix but perhaps ultimately a better long term solution since it makes for happier fish.
DIY CO2 to set up is dirt cheap. If you don't have too many plants I would reccomend using whole wheat flour instead of sugar in the generator so you don't overproduce the
CO2 - this can cause your pH to go down to far if it overproduces). Directions for
DIY CO2 can be found easily with a google search or her by searching past postings in this forum.
You could also build a small solar still which would produce about 2 liters a day of very soft water if you are in a sunny area (which you are). Again directions can be obtained online by looking up homemade solar still.
The problem with using the tablets or additives is that it can cause pH swings in your tank & is not a permanent solution (so its pretty hard on the fish in the long run).