Oh wow I never considered changing up the diet, seems really important. Unfortunately, I also believe it was fin rot cuz he passed away about an hour ago. Just for future uses, how would I go about fixing the nipped fins on top of the added medications cuz that seems like an environment thing or was it because of the amount of males in the tank? Tbh, after this large die off of fish from disease, I made it a priority to get some sort of water testing; idk why I never did it from the beginning. When I first got my tank, I put a few feeder minnows in it for a couple of months and once It felt ready, I went to the store and started with neons for a couple of weeks and then guppies.Hello! Thx for filling the template out.
Not directly related to sick fish but I would change the diet. Tetra is a "Junk Food" brand. Omega 1, Northfin, and Fluvle are some better food brands. Frozen is also a good option. Fish like variety just like people. One thing I noticed right away is you have way to many males per female. You should have a 1 male to 2-3 female ratio to stop overbreeding in your girls and aggression in your males. You have plenty of room in your tanks, I would add 6 more female guppies once you get him feeling better. If you have a breeder net I would septate him in that or even better a quarantine tank, you don't want whatever he has spreading to your healthy fish or him to further get picked on. To me it looks like fin rot from being nipped, that will cause the droopy body and clamped fins. Stress can also cause discoloration or color loss. Personally I would treat him with API Fin and body Cure and APt Stress Coat. Also make sure water is pristine. You will need to test your water to check parameters. Most pet stores will test it for you for free. You can also buy less accrete test strips but I personally would just buy a test kit, then you will have it. How did you cycle your tank?