Very Sick Betta: Attempt to save it? Or how to humanely put it down?

My betta's condition has been rapidly decreasing over the past month. He has had a strange kind of tumor-like growth on his tail that didn't seem to be much of a hindrance when it first showed up about two months ago. Recently, though, he's been acting really strange and has developed a LOT of other ailments. For the past two days, he has been sitting at the bottom of the tank as pictured with his head in a moss ball. He looks to have a pop eye on his left eye, some columnaris on his tail, is losing color on his chest, and today I noticed that he's beginning to develop dropsy. Is there any way to help him? I hate to see him suffer.

Specs: 10 gallon tank, only inhabitant, a little over a year old, tank cleaning done once a month, about 1/3 water change each time, all nitrite/nitrate/ammonia/pH levels are healthy, tank is about 80-82 degrees

Do a 75% water chang e immediately

What are your exact reading from the test?

I believe he is dying. I’m so sorry. You can euthanize him by adding 5 drops of clove oil in a small container of tank water. Shake it well. Place the fish in a small bowl of tank water and then slowly pour the solution in a little at a time. He will drift off to sleep and eventually his gills will stop moving. Leave him in solution about 30 minutes to be sure he is dead. Secret is to do it slowly.

Sorry but it does not sound good, I think @Deanasue is right. It is never easy to take a pets life but that may be the best thing to do at this point.

In the future, weekly water changes of at least 50% might help prevent disease

You can try doing some big daily water changes (using dechlorinated water) and gravel cleaning the substrate. He might recover but he might be too far gone. His health probably declined due to poor water quality, which was caused by lack of water changes.

As JiceBox mentioned, bigger water changes done each week can help fish live a long healthy life and not die prematurely.