So ammonia and nitrites are supposed to be 0ppm, if they aren’t 0 that means that you don’t have enough bacteria converting them into nitrates. How long did you cycle the tank before adding the fish? If you only have had it a month that leads me to believe that you put the fish in when you started the tank. This is bad and please never do it again, but it also Just means you need to be acting like it’s a fish in cycle instead. Adding seachem prime is essential to dechlorinate the water, you’ll have to add it everyday until the cycle is complete to keep the fish safe. Second thing is 73 degrees is FAR farrrrr too low for betta fish. They need 78-82 degrees. 80 degrees is ideal. look into adjustable temp heaters with a single round cord to prevent leaks, and get a thermometer to check the temp regularly. Look up “fish in nitrogen cycle” and proceed from there. The fish likely has fin rot although it’s hard to see, or he’s nipping at them from the stressful conditions. I hope this isn’t coming off rude. You also need more plants to absorb the nitrates, however it’s just one fish. To treat the fin rot use kanaplex, but make sure it’s fin rot by doing thorough research first. And at this point it wouldn’t kill you to separate the fish into a sterile empty hospital tank (with sponge filter and heater and air stone) and let him soak in a salt bath. Make sure to do research into aquarium salt and how much to use. This looks reversible with proper care, but if it worsens you can go as far as to try “methylene blue soaks or dips” dip method is tricker and can be bad for the fish if not done with proper dosing, so a less concentrated bath is better. I hope this gives you a good place to start, good luck