How to raise pH?

Question
I've built a small pond system (~2000 gallons, no fish yet, bio & UV filters, mostly shady area with pine & oak trees all around, NW Florida (don't know the temps yet, 3 feet deep) with waterfalls in the back garden and would like to place koi in the ponds. Plants (lilly pads) and frogs appear to be doing well (population increasing).
I am using well water to fill the ponds, and the local fish store digital pH test came back with the well water out of the tap with a pH of 4.7, and the pond water about 4.65. All the other markers came back neutral (no ammonia, I don't remember all the other things they said were OK). The pet shop people suggested I fill the ponds with tap water, but that gets to be an expensive proposition, and I'd still have to test pretty often to keep the tap water balanced and negate the bad things that come with tap water.
I've read that baking soda and ground limestone can be used to raise the pH, but the article didn't mention how much to use. Do you have any suggestions?

Answer
Dear Dan,

Thank you for your question.
The best way personally to go is for example to ad tap water as often other products are, when all put together, higher in cost.
Also salt (natrium bicarbonate) is used to stabilize the PH value.
Other possibility is to add PH plus products from the pond stores.
Advise is, when fish are in the pond, to add very little at one time as you may know, 1 degree higher is 100 times change for fish. So higher the value max 0,5 at one time to keep fish healthy.

Good luck!
Kind regards,
Raf