I have been struggling with keeping my water chemistry balanced. I have a 10 gal. tank with only a male betta left.

I guess I have had the tank for 3-4 mons. My biggest problem was the ph. I use the quick dip water strips (but will purchase the master kit that I have read about on this site).
About 3-4 weeks ago I did a complete water change. My betta stopped eating & seemed stressed. I refilled the tank using start right to remove chlorine, stress zyme & bulls eye for the ph. I tested the water & everything was right.
The water has been cloudy for a few days & when I test my water with the strips, everything is in balance except the alkalinity is high (300). My ph reads neutral 6.8-7.2. I don't know how to fix the alkalinity. My nitrate & nitrite are both reading safe. My water is usually always hard but is between 75-150 soft-hard.
I think the water may be cloudy because it is cycling but I don't know for sure. I am also wondering if I should be using an air stone for oxygen in my tank? I change the filter every 1-2 weeks, is that to often? The filter I have is the one that came with the tank. I really like having my tank but it is very frustrating to lose fish. I will not buy more until I figure this out.
This site is very helpful & I appreciate the help. Thank you.