Ph is the least of your worries, with a betta its really not going to cause a whole lot of issues unless its super, super high. 7.8 is fine.
You should be right in the middle of your cycle, so your probably experiencing some sort of spike(which can be harmful or even deadly to your fish). The testing material you have isn't accurate, so your not getting proper readings...if you can't afford the API kit, you can take a sample of your water to you LFS and have them test for Ammonia, NitrIte, and NitrAte....just be sure they're using some sort of liquid dropper test kit if not the API brand, and ask for exact numbers. Though taking a sample of water every day would be kind of a pain....you'd probably be better off just buying the kit yourself...in the long run it'll save you a lot of gas money and you have it right there if ever theres something wrong and you need to test your water.