Welcome to the forum! Sorry it's under these circumstances though =(
It really does look like it. The black edging could be his natural coloring, but with the black and the shredding, then I'm going to go ahead and say it's fin rot.
The conservative way is with Aquarium Salt.
What you are going to do is:
(Since unsure his tank size and what is in it, I am going to recommend putting him in a QT tank/container. If you have a 1 gal, use that, or a tupperware container free of soap residue where you can float/tape in his tank to keep the water warm. Some even use the cup they are purchased in. If using something less then a gallon, get a gallon water jug (empty out any water from there that isn't tap (use tap) - again don't use soap) and fill it with this:)
2 teaspoons per gallon of Aquarium salt (dissolve it well prior to adding in fish as it can burn them if it isn't), along with your regular water conditioner or Stress Coat. (You can also use your regular water conditioner with a little bit of Stress coat as Stress coat helps promote fin regrowth and will help keep him soothed while in the QT).
100% water changes daily for 10-14 days.
You should start seeing white to clear coloring on the edges of the fins which means the fins are growing.
If by the 14th day it's still falling off/crusty let us know and we can go with something a little stronger.
May I ask the size of the tank, and how often you change your water and the % you change?
Fin rot happens when a fish splits or damages a fin and the water is dirty/unfavorable so the rot forms. We may be able to help you prevent this in the future.
So today I woke up and he was WORSE! AND THEN!!!!! when i looked really close under the light there were these little parasites ALL IN THE TANK! I quickly did an 100% water change and used a reserve two gallon tank to put him in and used some stress coat, aquarium salt, and Betta revive. And other suggestions you can make? What kind of parasites would grow in the tank and most importantly WHY?? We change the water every week and are VERY careful! I just don't understand. We have a filter, heater and 5 gallon tank. We don't really do 100% water changes just two gallons every week. I have no idea where these parasites came from.
Were they little white worms? If so, most likely Planaria..
Planaria are often found in aquariums with uneaten food. The planaria won't hurt the fish, but they are a symptom of too much gravel containing too much uneaten food, and that is not good for fish. They require a food source, which means there must be excess food wastes in the tank to support them. The parasites that are in/on a fish always need a host to survive, so they wouldn't be free swimming in the tank.
Treat him for the fin rot as I mentioned above (2 teaspoons per gallon of Aquarium salt (dissolve it well prior to adding in fish as it can burn them if it isn't), along with your regular water conditioner or Stress Coat. (You can also use your regular water conditioner with a little bit of Stress coat as Stress coat helps promote fin regrowth and will help keep him soothed while in the QT).
100% water changes daily for 10-14 days.) and remove the betta revive as it's not needed and putting AQ salt in with any medicine can harm/kill your fish easily. Should never mix AQ salt with medicine.
Do 50% water changes per week, using a siphon to clean out the gravel as well to help prevent those from developing. What are you feeding him and how much?
well we used to feed him the blood worms and we have stopped that since they just fall straight to the bottom (to be lost in the rocks). So now we just feed him the betta pellets. SOMETHING was eating away at his fins cause he used to be a beautiful butterfly betta with quarter inch white around the tips of his fins and now he has none! And the blue is so shredded now too. I feel so sorry for him. If there Planaria are harmless then what what eating away at his fins?!
That is why you have planaria.. a good habit to get into is feeding them their food (blood worms included), is one at a time to make sure he eats. (You only feed 2-3 worms at a time as it is.. and that is only for frozen.. freeze dried you shouldn't be feeding all that much. Also for pellets.. 4-6 medium sized pellets spread between 2-3 meals.)
By feeding them the correct amount, and doing it one or two at a time you can make sure all is eaten and remove any that isn't to prevent this.
As for the SOMETHING... bettas can and many, many do.. bite their own fins and chew off pieces. But the pictures look just like fin rot (which could easily of happened since you have enough in the tank to support the planaria), you have a 5 gallon and doing water changes weekly, but what is the % you are changing?
Just stick with the treatment I mentioned twice and it will help him. It's an advanced case almost, so I would do it soon. He has fin rot, and that is what eats their fins. That is what is eating his fins. Rot. It is rotting off. =(
Ideal is 0 Ammonia/nitrate/ites. Sometimes meds don't always work.
Some suggest both Maracyn 1 & 2, but the most common way is through the salt treatment I mentioned, and when it comes to meds, API Tetracycline, API Fungus Cure, API Triple Sulfa, OR API Erythromycin are recommended for rot.
Just don't mix the AQ salt with any medicine.. use one then the other. Right now I'd try salt as to not piggy back the meds since meds aren't really all that idea for fish and to avoid if possible. Why most of us here will offer the conservative treatment before medication.